I run an older android version, no google apps, rooted, and use AFWall/AdAway. I’m sure it’s not as secure with root and older software but I can mostly trust it to not send weird network packets etc.

btw my work website also checks if i’m active/focused on a tab or if I clicked off it, this addon spoofs it well https://addons.mozilla.org/en-US/firefox/addon/always-visible/