It does seem odd for those "low code" tools to not have a way to deal with "external users". For example, it would be logical to create a tool for accepting job candidates. The internal facing piece would be limited to some reasonable number of users, but the outward facing piece would have to allow anyone to submit a record.
I do know that knack.com has a pricing model based on number of records instead of number of users. Might be an option for you, depending on how many records you have.
Airtable does allow you to create a publishable form view so that anyone can submit a new record.
You can also add read-only users to a base without having to pay for them. But giving them any kind of edit access (even just the ability to add comments to records) requires a full-fledged user account.
I do know that knack.com has a pricing model based on number of records instead of number of users. Might be an option for you, depending on how many records you have.