Aww, ‘Admin’ users. There’s a way to restrict who can add certain blocks to the site but I’m not sure if that ‘retroactively’ means they can’t edit existing Form blocks. Dashboard → Stacks and Blocks → Block Permissions. Click on ‘Add block’ and then on the ‘Details’ tab in dialog box. Right now, it’s set to ‘All Block Types’ so choose ‘Custom’ and all the blocks available will be presented. Check all the blocks that you WANT admins to be able to add so leave ‘Form’ unchecked. On my list, ‘Form’ is at the very bottom of that list. Now, as I say, I’m not sure if that restricts Admins from editing existing forms and TBO, I don’t have a site I’m willing to experiment on. Messing with the Admin group isn’t something I do often. I’d think about adding a new group like ‘Site Editors’ rather than try to restrict Admins. I usually only have 1-2 Admins and the rest of the ‘power users’ are ‘Site Editor’.
Similar discussion here: Advanced Permissions and Block Types