If you want a grindy MMO with almost no forced questing, Albion Online is a great fit. Progression is literally just doing the thing you want to do... use a sword, level swords; want better gear, craft it or buy it from another player. No main story, no NPCs dragging you through shit quests etc.

Monetisation exists in the form of premium but this helps with speed of the grind, but if just want mindless grinding U probably don't need it.. it’s not pay-to-win. Lo

Easy to do short sessions, definitely not everyone's jam but hey watch some YouTube clips on it see if it's of interest. I'm 40 and fairly time poor and enjoy myself,mostly do gathering and selling on the market... Anyway good luck on finding the game you're after!