mmmm
I use my two old iPhones (one Xs, one 11 Pro) as WiFi hotspots.
As long as they get security updates from Apple, it's okay.
And of course I use the lockdown mode for the iPhones, because this doesn't affect the reasonable use of a smartphone at all, but makes attacks and perhaps also adverts/telemetry more difficult.
Two Pixel Phones use only the internet connection of these hotspots (sometimes).
Also my MacBook Air M2 gets internet connection from these hotspots regulary.
But no exchange of other data.
I use and recommend Private DNS functionality. I am using NextDNS for it and have given all my devices their names as prefix in PrivatDNS URL, so I can filter them in the dashboard of NextDNS in Safari browser (statistics tab).
I use excellent blocklists in NextDNS, so that most spam, known malware and telemetry data are not allowed through.