>>96019013
Ok, I'll do the work for your lazy ass.
>LoL
https://support-leagueoflegends.riotgames.com/hc/en-us/articles/4405781372051-MMR-Rank-and-LP
Here Riot clarifies MMR and LP are separate. LP decays, MMR does not. When they mention decay in https://support-leagueoflegends.riotgames.com/hc/en-us/articles/4405783687443-Placements-Promotions-Series-Demotions-and-Decay they specify LP decay.
>Dota 2
Apparently they started using a new system a few years ago, see pic related. https://esportsinsider.com/dota-2-ranks
Their "decay" is just an adjustment of confidence, you still need to actually play games to calibrate.
>Overwatch 2
Once again, they have a separate MMR (hidden) and rank(visible). See https://gametree.me/blog/overwatch-2-matchmaking/ and https://gametree.me/blog/overwatch-2-ranks/
They supposedly use a system where there's a different set for each different role, but the premise is the same. Rank can decay over time, MMR does not.

So no, not a single one of those forcibly change your mmr over time. Most games will use a two part system, MMR in the background for actual matchmaking, and some sort of public facing rank so that people can show off their shiny icons instead of looking at a number. Sometimes devs will refer to the latter as MMR, because a large portion of their audience is retarded and doesn't understand the difference. Once you actually dig into how things work though, you see they never use the public rank for matchmaking, unlike MMR which literally stands for MatchMaking Rating. You can look at chess for an example of a game where they don't have a separate "rank" system, they use Elo rating directly.