Hello,
I am experiencing the same problem with several websites.
I have for now reset all of them to version 2.8.3 which makes them work again. I do not have any HTML field in my forms by the way.
Did you clear your browser cache and the caches of any caching/optimization plugins/services after updating to 2.9?
Caching and optimization plugins (e.g. WP Rocket, WP Fastest Cache) and services (e.g. host provided, Cloudflare and their Rocket Loader feature) have been known to cause issues like this. We recommend excluding pages that include forms from those features.
See the following page of the documentation for more details: FAQ on Cache and Script Optimizer Issues - Gravity Forms Documentation
If the issue remains once the caches are cleared and the page is excluded from optimization, the next step is to perform a conflict test following the steps described here: Testing Theme/Plugin Conflict
Note that for a valid conflict test, a test must be done with only Gravity Forms enabled. All other plugins, including third-party add-ons for Gravity Forms, should be disabled, and a default WordPress theme without custom code should be used (e.g. Twenty Twenty-Four).
If you don’t feel comfortable doing this on the live site, try creating a staging clone or sandbox setup for testing.