There are quite a few of them - either basically puzzle solving ones, scoring against a benchmark, or “defeat random events from a deck”.

Most modern board games have a solo mode and many games are solo only. I gave some links to the sibling comment if you want to look at some games.

Of course, who doesn't like playing with themself?

Seriously, though, there's a wealth of games for solo players! Some are made specifically for soloability, some have solo modes, some are older titles that have had solo modes written for them in retrospect.

It's a very interesting little niche and I think there's a ton of room for growth in it. I'm excited to be part of it as a player and to hopefully push the envelope a little bit on what can be done!