How to know how much recent activity has been seen by a person having access to my Gmail account?
If you used Chrome for Android as your phone's web browser, you should be able to view its history by opening Chrome on your desktop, going to History, and selecting "Other Devices" (also requires you are signed into Chrome on your PC, and, I believe, a sync setting enabled in PC Chrome).

For other apps, though, most do not retain any such logs, let alone provide a mechanism for remotely accessing them.

(Keeping an activity history on the device itself would be impractical due to the limited write lifecycle of the internal storage; Chrome retains your browsing history in the cloud as a convenience.)