After spending a lot of time in Google, I realized that it was about some descriptors
I haven't used descriptor wallets yet, but
achow101 on
Stack Exchange gives this solution:
The migration tool has not been implemented yet, and it is not for manually importing keys. Rather it takes an existing wallet and migrates everything in that wallet.
As the error message says, descriptor wallets do not support the importprivkey. You will have to use importdescriptors with the private key you want to import as part of the proper descriptor.
For example, if you wanted to import the p2wpkh address for a private key, you would make a descriptor of the form wpkh(<privkey>). Then use getdescriptorinfo to get the checksum and create wpkh(<privkey>)#<checksum>, and then use importdescriptors to import that descriptor
Or maybe you can still create a New Wallet and untick Descriptor Wallet.
I have a seed phrase, can I somehow import it from electrum? Or convert to a suitable bitcoin core format