In other words is the electrum wallet file (not software) GUI/software independent?
No, it will only work in Electrum.
It has its specific format and encryption algorithm that will only work in Electrum or clients that specifically designed to import it.
For the latter, Sparrow can import its keystore but it has to be Standard / MultiSig and not 2fa wallet (
and for some reason, it has to be encrypted)
Can I open wallets created with other BTC clients with Electrum too?
No, there's no defined standard on bitcoin clients' wallet file's file structure or database.
Every wallet developer used/created what they prefer.
What If a user wants to migrate from one BTC GUI client to another?
The desktop GUI has a hidden console tab which can be used to export what the GUI menus can't. (
e.g.: master private key)
If you're limited to the menus, then your addresses' private keys are good enough, and as mentioned by others, some wallets support Electrum's seed phase.
But the best way to migrate is to "
send max" to the other wallet if you still have access to Electrum.