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The thing about Electrum seed phrases is that their major difference is in how the seed phrase itself is generated, and not in how the seed phrase is used to generate private keys. Just like BIP39 phrases, they still get paired with a salt using any additional passphrase (if one is set), they still go through 2048 rounds of HMAC-SHA512, they still generate a 512 bit seed number, and they still derive private and public keys in the same hierarchical manner. Literally the only difference is they use the word "electrum" instead of the word "mnemonic" in the salt, and they use a different derivation path. Therefore, any open source BIP39 wallet or code (such as Ian Coleman's site) can be changed pretty trivially to accept Electrum phrases and generate the same addresses as Electrum itself would.
Not that trivially because even though it may not like it but there are two major differences between the two algorithms. BIP39 simply uses a single SHA256 as its checksum which it will append to the end of the 128-bit entropy (assuming 12 word only) while Electrum uses an actual 132-bit entropy and increments it until it finds one that has a HMACSHA512 that starts with a certain bits.
That's not even the biggest difference, the biggest is in string normalization. BIP39 uses a simple KD normalization while Electrum significantly modifies the strings if they aren't plain English words (that includes the passphrase).