The first is you set a passphrase and do not remember doing so. A passphrase can be any combination of letters, numbers, or symbols. Perhaps you mistakenly thought you were setting a password for your Trezor Suite software. You could try any common passwords you frequently use, or you could also just try " " (i.e. a space) in case you did something like this by mistake.
I like this, and it's entirely possible that someone not that familiar with the terminology could mistake a passphrase for a password that protects access to the software. OP even said he didn't know about passphrases at the time of the setup and only found out about them by doing research for the issues he is currently experiencing.
Trying out common passwords you usually set (assuming you are using the same or similar password combinations) might help. What would happen if he started the passphrase generation, noticed something was off, but added a passphrase by mistake without entering a single character? Is that even doable?