You are using your FP3 to provide a Wi-Fi access point for some other device(s) (PC, Mac or whatever).
I would advise you to turn OFF Wi-Fi on the FP3, leaving only Mobile Data enabled.
In the Hotspot configuration, which security option are you using?
Lastly, the seemingly absurd “turn it off and then turn it on again” may help (with “Extend compatibility” disabled). Also, disable the option “Turn off hotspot automatically”.
As a work-around, have you considered using Bluetooth tethering instead (or maybe this isn’t an option)?
I turned off Wifi, tried all security settings, including no password, and
disabled the automatic switch-off, to no avail. The only thing that helps
is either switching it on and off and on, or extending compatibility.
Since this is a new freshly installed phone, there might be some setting
that makes it work for you.
Regarding Bluetooth and USB, I’d like to use that but somehow the kernel
modules for the latter were removed recently, while the former didn’t work.
I suspect that most people use Wi-fi rather than USB or Bluetooth, so I’d
expect this to work more reliably in principle.
Regarding USB tethering, to be more precise, according to https://lkml.org/lkml/2022/11/23/1502 the RNDIS linux module used for USB tethering was deprecated and removed from the Linux Kernel, also of my distribution;
in favor of Network Control Model (NCM), that however only works for Android 14 and beyond, whereas my Fairphone still uses Android 13.
Good news is that Bluetooth tethering started working again, so I’ll stick with this for now.
I have also had issues with my FP3+ since the Android 13 upgrade. It became almost unusable but gradually improved with each update since. However I still have an issue where when I turn on my phone at the start of the day for example, none of the apps or phone works and I have restart it for everything to work again. After the initial upgrade I had to restart it at least 3-4 times before it finally worked so it’s an improvement! But still not ideal. Any ideas on whether this can be fixed? Thank you.
In-place upgrades of major OS versions can cause trouble on any device with any OS. Installing the OS from scratch will either remedy the issue or at least make sure the upgrade process didn’t cause it as a valuable troubleshooting step. A factory reset is a worthy try beforehand because it’s quickly done and might already help, but it only deletes user data as well as Apps installed by the user and their data, it’s not a complete device reset.
Your data would be wiped in either case, be safe with a backup.
A very belated remark, but might be useful to other readers:
Compatibility mode means 2.5 GHz. This is now the only option for Wi-Fi hotspots generated by mobile devices, since a EU directive of 08/02/2022 forbade the use of 5 GHz outdoors.
The directive was applied in A13 or maybe A12.