pathfinder

I started playing after they had announced but before they had released the remaster, using the Core Rulebook from before the remaster. Personally, I don't find it a problem at all. Unlike D&D the remaster is very surface level. It maintains basically perfect backward compatibility, not just "compatibility if you really need it, but you'll really need to upgrade as soon as possible by buying our new books".

As long as you have a general list of the changes. That you know things like "flat-footed became off-guard", "attack of opportunity became reactive strike", how ability scores being used to calculate modifiers changed to just have the modifiers, and the removal of alignment in favour of sanctification. There are other changes, like minor tweaks to classes and a bigger overhaul of spells—especially cantrips, some of which are changed, while others were renamed and changed (where the intent is that you should only use the new renamed version, but they specifically wanted people to easily have the option of staying with the old one). But outside of a small list of over-arching changes that become relevant when reading older material, it's mostly just a really big errata/balance pass, and whatever version you're using will work fine.

Plus, because all the content is available for free on Archives of Nethys or the various tools like Pathbuilder, Demiplane etc., you'll be able to see the latest version of everything. At that point, the only thing that's relevant is knowing about the verbage changes like off-guard and the ability score changes. Everything else, you can just use as written.