MSFS2020 (only-game pass cancelled)

You can cancel your subscription and just purchase the game to continue playing it. If you only cancel Game Pass, you will no longer have access to the game.

As stated in your original thread, yes. As long as you own the game, you do not need Game Pass.

You can cancel game pass by going to
account.microsoft.com, select services & subscriptions, scroll down to game pass, select payment & billing under game pass, then select cancel. That should cancel your game pass for you.

the only option available is to pay and they say that they owe them a month or something

Only if you purchase it. Otherwise if a game is removed from game pass, or you cancel game pass, you lose the game.

You can only convert it to Ultimate if you purchase Ultimate. The only way to convert it to PC Game Pass would be to cancel it and purchase PC Game Pass.