jinjal, popular VPN's are probably tracked by your government. You'd best have a cloud provider host a VM with a static IP. Install your own VPN to connect there. Host the VPN on port 443 or whatever else a security professional suggests that is smarter than I.
jinjal What Data will be saved/generated and where if i connect a GOS-Phone to a wifi?
This is the same as some one asking: "What if my windows computer...?" or "My HP laptop has an issue..."
People perform a variety of tasks on their computer that do not relate to HP or the operating system. Most likely the same is true here too without reading anything they wrote.
OP asked "what happens if their [phone] connects to wifi and how to be safe." However, even if they literally asked "What info does GrapheneOS give out?" They are actually asking the former question. Most personal relationships and professions require answering the questions not asked. Only lawyers deal with semantics about: "technically they said GrapheneOS and not 'my device' ".
Johnnyloans All depends on the apps you have installed.
Onlyfun Does this mean use of graphene os will be revealed per OP concern?
Onlyfun Applies to first quote of yours as well, no?
OP didn't ask if any one will be aware of the operating system on their phone.
I don't know anyone that doesn't install apps on their phone nor log into any service. Besides, let's assume this is true and OP won't do any of this.
Onlyfun Wi-Fi on GrapheneOS is very privacy-friendly and is essentially anonymous as long as apps do not leak uniquely identifying information to the network.
Correct, grapheneOS won't leak any info about you. However, I don't go around telling people to install GOS then you cannot be tracked because no one will get your name and phone number--do what you want on the phone.
The phone has call and texting baked in. OP won't call or text anyone? Won't log into any form of communication? The phone number is unique to their person as is any accounts. The authoritarian government can obtain info from companies or even be in 100% control of the internet or cell towers.
With your purport of no leaking info, what's left for the the political activist do with the phone besides apps or any accounts unique to them? read news articles anonymously? They mentioned their desire to connect to public wifi. Are they adamant driving over to public wifi so they can connect to their homelab swarm of self-hosted services instead of Google?
Onlyfun Important to keep in mind that vpn only partially mitigates OP concern.
Onlyfun Isn't OP concern fully addressed in above mentioned 'default graphene os and bundled apps connections'?
This contradicts your first 2 statements that OP won't have apps or sending out anything unique to them and that their concern is answered by "GOS won't narc on you" but "GOS can still narc on you with a vpn." How would a vpn leak anything that doesn't exist.
In conclusion, OP does need to be mindful about what they do on the phone that has no relation to GOS.