I'd like to suggest an update to the achievement system to prevent (or at least reduce) loss of progress towards 100%-ing a game, this comes from frustration that has been building up from losing my progress on multiple games over the years (the biggest culprit being Risk of Rain 2).

At the moment, developers can add new achievements through updates and DLCs. This not only makes it so you can lose your 100% on games, but also locks some achievements behind paywalls without making a distinction between those and the ones from the base game.

While there is an argument to be made that this would encourage people to either replay a game or buy its DLCs, in my experience it just makes me frustrated with the developers for adding them (thus making me want to play less) and the way it is being handled and makes the achievement system feel janky instead of properly managed. Also I've never bought a DLC because of achievements.

I'd like to suggest a system similar to the way PlayStation handles achievements, where the distinction between DLC achievements and base game achievements is made, allowing players to get the platinum trophy (equivalent to a 100% achievement completion) without having the DLC achievements count towards this. Base game and DLC achievements are shown in their own list (on PlayStation when you click on a game it then asks you to select the base game or the DLC you want to see the achievements of)

I think this system could also extend to big free updates adding new content after the initial release of the game.

To give a concrete example, I had 100%-ed Risk of Rain 2 before its first DLC came out, then had to do it again after the first DLC came out, and I'm now fed up with having to do it a third time with the second DLC (which I don't like as much as the rest of the game) so any time I look at the game I just feel a bit annoyed that my time achievement hunting was wasted (especially since a new DLC is coming soon) and I feel like this could have been avoided by actually making this distinction (which as mentioned, PlayStation has been doing for a bit more than a decade now and I think it's fair to say their achievement system is the best one out there).

Had the achievements been properly categorized, I would have been able to 100% the game and the added achievements would have been a nice bonus that motivates to play the DLCs instead of doing the opposite by feeling like a waste of time.