I can relate because all of my friends for the most part aren't playing anymore and I'm from 2004 and have been playing the same world since then. I'm sorry to hear but I can definitely relate. To improve my gaming experience solo I like to focus on quests, achievements, bestiary, hunting and prey tasks.
I'd also try to invite back some of my old friends so if I were you I'd invite them back on tibia.com on your account page there's a section for that to try to bring them back. You can also get rewarded for using this feature if all pans out right.
Maybe I'd buy a new house to start fresh and decorate it for hours, sort my depot to keep busy, sell loot. All the lonely things you can do in Tibia. Oh what would be lovely would be for you to maybe join a guild, talk in English or World chat, check forums to see how you can make friends.
I also would try out new spawn so I'd suggest looking at these hunting spots to try to get new ideas:
https://www.tibiaqa.com/3367/where-to-solo-hunt-ek-270-for-exp-%26-profit
https://www.tibiaqa.com/9406/good-places-for-a-knight-level-250-to-make-exp-and-profit?show=9406#q9406
Being solo in Tibia can be very fun :)