It's not really a single single player game, more a set of specific genres: "Ubisoft open world", "Immersive sim" (especially Arkanes), "Bethesda RPG" (Even 76 which ye cna play pretty much solo), "Walking Sim" (a genre I fell in love with this past year)
I don't normally enjoy many walking sims, but something about the pacing and delivery of Firewatch nailed it for me. Didn't overstay its welcome and kept me interested enough in the story that I think I did the whole game in one or two sittings.
Stanely Parable is a great game. It has great replayability baked in finding all the endings and little things, with really solid and humorous writing.
If you're looking to just relax, have a laugh, and have fun trying to break a narrative, genuinely recommend it.
If ye want something short then A Short Hike (heh)
If ye want horror try SOMA
Scifi/Detective then Tacoma is pretty good.
Eldrich Undercurrents - Call of the Sea
If Atomic Heart vibed with ye then Paradise Lost.
I would recommend giving a check on steam to see if any of them catch yer fancy