Cryptpad has Forms. You can choose if users need to sign in. Looks like you don’t even need an account to create one on their official instance. It’s self-hostable too.

I like HeyForm. Here’s the source code, as well as instructions for self-hosting. It looks very clean and modern, and has a similar UX to Typeform.

The second best option would be Nextcloud Forms (source code).

mhm, nextcloud forms?