About signrawtransactionwithkey maybe it works, I heard many times we couldn't do taproot transactions without PSBT's, etc and I did it, so, maybe everything have solution and the problem is just doing the configuration of the command with all variables.
If someone have success please report it.
Contrary to the name
signrawtransactionwithkey, the command doesn't sign a transaction unless it isn't of the TapRoot-type, I'm afraid. I have verified it. There isn't any tool to do it.