Another option is a round-the-world backpacking trip, or something like that.

But these are much easier if they're already hobbies or interests.

I can highly recommend backpacking, OP. Especially if you haven't travelled before. Solo exploration of countries and cultures is a constant source of wonder, and you'll meet amazing people along the way. Setting your own agenda in a foreign land and putting responsibilities in your own country on hold is really liberating. It will give you an opportunity to assess what's important. Hostels are full of people doing the exact same thing and you end up making close connections with folk.

Backpacking has been hit hard with covid though. As I understand it, hostels currently aren't quite what they were before the pandemic. And fear around this new variant will keep it that way for a while. Next summer things might pick up enough to explore Europe and beyond though, fingers crossed.

Similar-length hiking options exist in the EU, like Via Alpina. Adjacent suggestions for long-distance and/or solo tourism are worth considering.

With the luxury of time, investing in oneself can be done in novel ways, e.g. flying or ocean sailing, triathlon, surfing, craftsmanship, golf.

I was going to recommend something similar. Finding one's connection with nature can be extremely fulfilling