I'm going to post a hot take. There's no such thing as modern RPG mechanics.
Here I agree somewhat. There are some modern mechanics but overall rpgs did almost not evolve because of different reasons.
I would still say thst there are some rpgs which use partially modern gamedesign. Because in the end RPG is also a game and rpg mechanics are modern if they use modern gamedesign.
With RPGs we still see rules and mechanics similar to those we used 20, 30 and 40 years ago coming out in new RPGs. Yes, there are new ways RPGs do things, like having a narrative focus, player facing mechanics, etc., but that doesn't suddenly antiquate the other mechanics that are still in regular use. It just means that there is a greater variety of modern ways to create RPGs.
Its a sad thing that we still wee the same old mechanics and it has to do with the fact that in rpg design there is just not that much money to get and that RPG players have lot of nostalgia and dont like change. and also thst there is 1 game which has such a huuge market dominance that soo many people just copy it.
Whether it's intended or not, and I think it's mostly unintended, calling the newer methods modern is very subtle One True Wayism. Modern is the good way and should be embraced, and the other mechanics are for the ancient grognards that shouldn't have games designed for them anymore. Never mind that new games with older mechanics get new players.
Well gamedesign overall evolved a lot the last 40 years. Yes some people still play monopol (often people who dont know many boardgames), but pretty mveryone who has played 50 or more modern games agrees that monopoly is just a bad outdated game with outdated mechanics.
Also often old things, even if they qre outdated, get new fans because they are still popular (at least in parts of society). People watch popular things and play popular things because others do it. Even chess, which is okish, would if released today be played by no one, because modern game design evolved so much. (Chess only works at all because it has 100 000s of players. Because it only is fun/makes sense to play in such a narrow skill gap that its hard to find similar level players. And the lack of variety even brought discussions into high level chess to change start setup)
I am really glad that in boardgaming the players were not so averse to changey and allowed to have today 188× different boardgame mechanics, and we are not left with roll to move.
If players want old mechanic, why do they then need new games? They can just play the already existing old games with old mechanics.
There were always games whigh looked into modern gamedesign and took some inspiration from there. Of course the big one was Dungeons and Drsgons 4th edition, which tried to apply precise gsme design to all aspect of it.
Using clear modern game design language for abilities, as is the game industry standard (MtG like wording which most modern boardgames and computer games use). Which includes use of keywords and tags.
Codyfing things, to make it clear design goals not just accidents like the roles.
Cresting a setting gameplay first. If its not needed or msde for gaming its left away.
Streamlining mechanics (like boardgames, modern eargames etc. Do). Like Having uniform representstion since that makes it easier to learn new classes. (Which is ehy this is used in all modern class based gsmesy shooters mobss etc). Reduving mumber of skills, making skills more defined to use (similar to hoe PbtA plsyer "moved" look).
Thinking about how to use mechanics to make it easier in play. (Cards for tracking "vancian spells" (and conditions eith the card), non eucledian movement, having squares directly not "feet").
The bad reception of its modern gamedesign in 4e (often by people who were not familiar with modern games) Unfortunately threw RPG design back by 10 years, glad 5.24 at lesst used again a bit more 4e influence
Still we fortunately do get nowadays some games with some modern gamedesign. Sure still most use dice resolution ss its main mechanic, but we see othet thigns at lesst
- Legacy mechanics in Yazeebas Breakfast
- mission based combat design with alternative goals like in Beacon (or Lancer and Draw Steel)
- illusion of choice design from Pathfinder 2 and Dragonbane. (Making one feel thst one has a choice is for many people more important than having one.)
- deckbuilding to customize your dive by gloomhaven RPG (which can now be read)
- codyfing and separating combat roles by Strike and Wyrdwood wand.
- Solving specific problems like alphastrike problem with escalation dice in 13th age, or the "always repeating the same when using ressource based approsch" in trespasser.
- allowing to get rid of the GM in more narrative based games like Alice is Missing or Ironsworn as well as in tactical games like Emberwind.
- even just actually using specific physical components to improve gameplay (coming away from the idea that the only components should be paper a pen and dices) like cards getting more common is great to see.
Of course the process would be A LOT faster, if D&D the huge marker leader would again be more daring, but unfortunstely this wont be the case.