Hi,
I think you mean disabling Related menu?
I think you cant hide this option completely, however you can get rid of all items shown inside related menu.
Note: This will also include important administrative tabs like Background Processes and Audit History as well. So if you are getting rid of all options it will be good to maintain 2 different forms, one with all the related entities on (for admins) and one without them (for non admins).
You can open your form in power apps solution for customization and then switch to classic mode.
On the classic form customization UI, select Navigation option from top.
Then on the left hand side menu, remove all related entities from navigation. The empty one looks like follows (Navigation options removed from all sections like Common, Sales, Service, Marketing etc.).
Save and publish the form.