Also... do you know a safe way to find my master public key only using my wallet.dat and my password?
Even if you can compute it from the dumpwallet output's master private key,
Electrum wont be able to import the correct addresses since Bitcoin Core uses "
hardened addresses" which Electrum doesn't support.
That includes the master private key itself.
Only if it's a "
descriptor wallet", that could work with Bitcoin Core's
listdescriptors and Electrum's
convert_xkey() commands.