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 Google Workspace Marketplace add-on.
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.