It is truly upsetting to see how few people use password managers. I have witnessed people who always use the same password (and even tell me what it is), people who try to login to accounts but constantly can't remember which credentials they used, people who store all of their passwords on a text file on their desktop, people who use a password manager but store the master password on Discord, entire tech sectors in companies locked to LastPass, and so much more. One person even told me they were upset that websites wouldn't tell you password requirements after you create your account, and so they screenshot the requirements every time so they could remember which characters to add to their reused password.
Use a password manager. Whatever solution you think you can come up with is most likely not secure. Computers store a lot of temporary files in places you might not even know how to check, so don't just stick it in a text file. Use a properly made password manager, such as Bitwarden or KeePassXC. They're not going to steal your passwords. Store your master password in a safe place or use a passphrase that you can remember. Even using your browser's password storage is better than nothing. Don't reuse passwords, use long randomly generated ones.
It's free, it's convenient, it takes a few minutes to set up, and its a massive boost in security. No needing to remember passwords. No needing to come up with new passwords. No manually typing passwords. I know I'm preaching to the choir, but if even one of you decides to use a password manager after this then it's an easy win.
Please, don't wait. If you aren't using a password manager right now, take a few minutes. You'll thank yourself later.
Open a bug report in KeepassXC's repository, maybe it's a big in their code. Or they'll tell you that the bug is in proton pass, and you can report it there too so that they know about it and can fix it. Maybe the KeepassXC team can give you a workaround too
My English is very poor for technical explications.... I search the issue in KeepassXC Github but I don't found similar solution.
Proton Pass is a pretty new service, maybe there haven't been much users yet who have moved to KeepassXC from it. I would say give it a try, it's not that bad.
Something else you could try is:
a) check the Bitwarden repo if anyone had a similar problem as you. If so, it's more likely that it's a Proton Pass problem, and maybe they have some tips.
b) import your Proton Pass export to another password manager (Bitwarden, original Keepasd), export it from there, and try to import this in KeepassXC. Though this might have a higher chance of losing some information, in the sense of metadata. If you go this way, don't forget to make a fresh export of your Proton Pass account, in case you have changed something there in the meantime