Link: https://youtube.com/playlist?list=PLWTCD_J8kOHOeW1u3MH0CyTPT...
There’s also this great tutorial making a uniswap clone that goes through the hardest aspects of onchain development.
Link: https://medium.com/coinmonks/programming-defi-uniswap-part-1...
Not just accepted and popular ones, but also on proposals and rejected ones. It’ll give you a taste of what people are thinking about and what’s upcoming.
And FreeCodeCamp has in depth tutorials for Solidity.
That's what I'd get started with.