I am in a similar boat, from what I can tell you can disable the Gemini app here[1] but if you want to disable it in Gmail and Drive you need to have an enterprise plan then you can disable it here [2]

[1] https://admin.google.com/ac/managedsettings/47208553126 [2] https://admin.google.com/ac/managedsettings/793154499678

Wow, thank you. This was buried deep (not an accident of course).

"Pay us more money, or be forced into using our feature" is a new sales tactic.

Support will give you access to [2] if you raise a case and complain.