The Bitcoin network does not support advanced smart contracts, or more advanced than it already has. Separate networks do support them, but they do not use bitcoin as currency. Sidechains, specifically, such as Stacks or Rootstock, while they do make use of the Proof-of-Work being done on the Layer 1, they mint their own tokens, which should be viewed more as altcoins than Bitcoin, IMO.
I looked at brief descriptions of quite a few L2 projects. Isn't there at least one or more which do not use new tokens, they are a "true layer on top" which helps give Bitcoin more powerful smart contracts? ....and all the transactions are securely settled in
BTC. Yes, I did see at least one of those, I think.