How to create a user without a password in Catalina?
I'm running macOS Catalina 10.15.2 and guest is a reserved name, so you cannot use it.

I also just created a new standard account without a password. Just didn't put in a password and followed through with the prompts appropriately.

Note: My Mac is not encrypted and does not have the T2 chip. Either or both of these may require a password to be assigned.

One thing you can try is in Terminal use the passwd command to change the password to a blank password. This worked for me on my system, however keep in mind the note above.