If it's gone from the play store that doesn't matter, you have it installed.

Breaking OS changes are a problem, it's true. Thankfully they basically never happen on phones (certainly if you have a phone that stopped updates ~4-5 years ago it will still work).

You're on HN. You should say such blatantly false things like

"Thankfully they basically never happen on phones"

There has probably never been a phone OS update that didn't break things. And not in a "technically something broke so haha gotcha! way"

Broken in a "half the apps out there need to be rebuilt with a new SDK version and/or deprecated or there'll be obvious bugs" way

It's true if you don't need to change device. In 3 or 4 years (my usual device lifetime) many non updated apps is no longer supported at newer os version.