I was trying some Electrum seeds from bitcoin quest on iancoleman BIP39 page but the page keeps saying invalid mnemonic
This doesn't surprise me due to Electrum generating/converting mnemonics in a different way from BIP39. You can actually edit the IanColeman source code and get it to spit out the Electrum addresses from an Electrum mnemonic... I did it on an older version of the code, but I assume it won't have changed too much.
One of the key differences is that the BIP39 spec (and by extension IanColeman tool) uses
a passphrase of "mnemonic" + yourpassphrase... whereas Electrum uses a passphrase of "electrum" + yourpassphrase.
I was thinking maybe the same seed works on BIP39 and Electrum might actually derives different addresses if it was generated by Electrum
So, yes... the same seed
mnemonic (ie. "12 words") will definitely generate different addresses, as that mnemonic will actually be converted to differents
seeds (ie. the actual number) by Ian Coleman Tool and Electrum.
This is why I always try to explicitly highlight the difference between a "seed" (actual number)... and a "seed
mnemonic" (words).