This article explains how to remove Form Publisher from your Google account.
If you want to remove the add-on from a Google Form, you have to remove the add-on from the Google Workspace Marketplace.
From your Google account, click on the menu at the top left side. Then, click More from Google Workspace Marketplace.
The Google Workspace Marketplace page opens. Click the gear icon > Manage Apps.
Click the three dots > Uninstall.
Or click Uninstall directly from Form Publisher add-on.
A pop-up appears. Click Uninstall app.