Embarrassingly, yes this is the only time I'm accessing the wallet again after initially setting it up and transferring funds into it. I didn't feel the need to test a restore prior to transferring funds as the set up had to make me enter the recovery twice.
I appreciate this is maybe rubbing salt in the wound, but for future, after you generate a new seed phrase and back it up, you should note down the first address in the wallet you have created before wiping/resetting everything and recovering from your written down back up, to ensure you made no mistakes and you can indeed regain access to the same wallet.
I'm 100% certain that it's the right seed. I've only used it that one time. I've only gone through the setup once, so I only ever generated one set of recovery seed, which I had written down on three sheets of paper.
In which case, if it is definitely the correct seed phrase, and you've tried accessing it via Electrum at all the possible derivation paths, then it does indeed seem as if you have mistakenly set a passphrase.
I have a lot of experience using btcrecover, so can talk you through creating a tokenlist file to widen your search if it comes to that.
That is definitely warranted and this has changed how I look at securing things in general.
Thank you so much, that is such a generous offer. I am quite beaten down from trying and I am not confident enough that I'll be doing the right configurations since I wasn't able to crack it with my best-guesses password list. I've been thinking of reaching out to wallet recovery services, since I'm sure they're much more equipped and knowledgable than myself.