Ko is not rare in beginner games. It is also not frequent. It is something that occurs occasionally.

Alternation is not obvious for board games. They vary and different phases of board games have or do not have alternation.

Players take turns to control locations to create unique positions. There can only be as many total free turns as locations, however a player can get an extra turn after that for each location they've lost control over.

If a location is connected only to locations controlled by the same player, that player surrounds that location. A group of connected locations controlled by a player are not controlled by that player anymore if it's not that players turn and the only other locations that group of locations are connected to are controlled by another single player.

When any player has no free or extra turns or can only control surrounded locations, victory is awarded to the player with the most surrounded locations minus the number of locations they lost control of.*

*One divided by the total number of players victory points are given to a player for each player they score more than.

I had a different experience as a beginner where kos were very infrequent and often didn't matter. Even playing as Single digit kyu most games go along without the players knowing when or how to setup a ko.
I disagree. Alternating play is so fundamental as to be assumed for any board game unless stated otherwise. While some board games have separate phases within a turn and some board games are asymmetric (like hare-capturing games), that doesn't change the fact that the fundamental design feature of board games is to take turns playing game-pieces. It's surely not novel. And preventing repetition of a board state is not novel. Scoring based on game-pieces is also a fundamental design feature of board games.

My point is that Go's novelty lies in the surrounding/capturing mechanic. This is what makes this game "Go" when compared to other board games. So it is ultimately the only rule needed to define what Go is.

"Free teire" is not an "issue." Suicide is not an issue. Territory vs area is not an issue. Seki is not an issue. Ko is interesting but the possibility of a draw is not a big issue.

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So what about the Ultimate Go rules? They aren't simple and don't solve something that's an issue. So they aren't very ultimate.

What is the Ultimate Go rule? It's: Go is a game where playing a game-piece on the last empty intersection of a grid that the opponent's set of directly connected pieces was connected to removes those pieces from the grid. That's it.

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Sometimes I feel like game players haven't played enough other games. Not just Go players but board and game card players in general.

You should play a greater variety of board games to realise that simultaneous moving or event-driven procedures occur besides alternation. Not every board game is 2-player abstract board game, for which alternation is common possibly after the game setup and until the, if any, scoring phase.

Indirect control of a group of connected locations depend on direct control of the surrounding locations

I don't see why the concept of a grid has to be mentioned. And the concept of a game piece or object doesn't seem necessary .And even if players played simultaneously it would still technically be go, so the debate on the normality of turning isn't too consequential!

Then if you want you can add in you must relinquish direct control of locations indirectly controlled by another player (capture), or scoring based on indirectly controlled locations minus relinquished directly controlled locations, but fundamentally it's about direct and indirect control of connected locations.

When I first encountered Go, without guidance against GnuGo more than 25 years ago, the entire board consisted of ko shapes, and it seemed like a battle of will to capture more than the bot.

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A good system naturally covers all corner cases without further effort.

Of course. But here, I made an assertion and you disagreed and are now trying to refute it. But for someone so keen on logic I'm surprised that you don't see why that the possibility of moving/event driven procedures in some games does not prove that alternating play is not a fundamental feature of board games.

There is a difference between alternating play being a fundamental feature of many board games and it being so universal and always-applicable that it would be obvious to use it at all in a particular game and always in that game.

In particular, a go game, as we play it, has an alternating phase and a determination-of-winner phase, which is (or for some rulesets, ends as) not an alternating phase. Therefore the rules must say that the players alternate and afterwards (end to) determine the winner.

Maybe this can be a contribution to the discussion?

https://www.kfchess.com/

Anyway, I think if you want minimal rules for Go it can be anything you like. Is the most minimal rules of Go simply the empty string, ""?

Have not played Chess for decades. Set novice level. Made essential typos but won anyway;)

Go
Indirect control of connected locations under the same direct control is given to the player with direct control of the immediately surrounding locations.
Direct control of connected locations are lost if it's not that controller's turn and they all fall under one different indirect control other than neutral.
So this is all that's needed to describe Go

Standard Scoring
When either a player has taken direct control of a location more than the total number of locations over the number of players plus the number or it wouldn't possible for a player to take control of two locations under the same indirect control simultaneously without losing control of them when their turn ends, every player gains one over the number of players victory points for each player they have a higher total of either: indirectly controlled points minus the number of times direct control of a point had been lost plus the number of times direct control of a location was taken beyond the total number of locations over the number of players, or: indirectly controlled points plus the number of controlled points. Or: the average of the differences in score from both methods.
This implies each player has 180.5 stones with leeway for other board sizes and numbers of players, which I think should be part of the rules, yet it doesn't make it necessary to count stones since turns can be counted instead.

Standard Location layout
(13+6n)^2d locations in a regular quadrilateral or regular hexagon, where n is an integer and d is 1
However in semi-standard sizes n and d could be any real number. The super standard standard is n = 1 and d = 1.

However, then again, ultimate Go doesn't include score in the rules--it's highly axiomatic and that seems more ideal. So the (perhaps a bit of topic) rules above should somehow be mixed with ultimate go rules, maybe . . .

Also the 'Ultimate' in ultimate go refers to the original meaning of the word of 'final' or 'last', it's simply a poetic pun that it can imply 'best'.