Which fritzbox do you use? Which firmware version is installed?
Does the guest network has an encryption set?
The first thing I'd think of is a WPA2/WPA3 problem. Just a quick guess.
I just applied https://gerrit.aicp-rom.com/c/AICP/device_sony_msm8974-common/+/109829 and will upload a build soon.
Besides that: A log would be helpful in any case.
I uploaded the new build now. Should also be offered as ota.
And one more question from my side: Do you use mac address filtering in your fritzbox? This could also be a reason, as the mac address was not consistent across the last builds.
I enabled WPA3 on my fritzbox as well and wifi broke as you decribed. By using the build I just uploaded it is working as expected again. Could you please try updating?