Not wise to lock yourself to an old version. Although legacy wallets still work fine in v25, by the way.

You can turn your custom entropy in to a master private key you can import in to a descriptors wallet as I explained above, but you won't be able to do it without additional software.

Alternatively, have you considered using something like Electrum or Sparrow instead? You can turn your custom entropy in to a BIP39 seed phrase and then import that to these wallets offline, and then export the master public key from your offline wallet to move to your other machine and create your watch only wallet. Your watch only wallet can be synced using your own node.