when i wanted to learn Solidity, at the time, I was really into yield farming. I forked the sushiswap masterchef contract and just played around with tweaking it. you can do this for (basically) free on a chain like BSC or Arbitrum or you can play around with forking a network using Ganache or hardhat (or Foundry if you are a Rust nerd).

Crypto Zombies is a very good interactive intro to Solidity, despite being REALLY outdated at this point (last i checked it was using Sol 0.5 or 0.4).

my best advice is find some popular crypto concept you vibe with and just start messing around. Vyper is also growing in popularity so that might be worth checking out too!