So, this is my experience with the issue.
I’m on a Xperia 10 III, in Italy, with Iliad as provider. I had never had any big issues related to mobile data, until recently. I roamed abroad, I used wifi networks in many different places, and never experienced any issue …fortunately. The only bug I faced was while in the USA, where I got an extra Ultramobile card that somehow did not get along well with my Iliad card, which could only work alone.
Now I cannot get Android apps to go online through Mobile data at all: only via wifi. I tried pretty much “everything” without the situation changing: I turned the phone off and on, I started only data service, I restarted ofono service, I erased its data and restarted it again, I reverted to Android (and used it to call, text, and browse), I reinstalled SFOS, and the issue is still here. BUT, the thing I remember doing before all this, I changed my SIM card: I had a normal one until recently, then I got an esim!
I know that Iliad is quite particular (data service is working fine right now, even without any input after another new reinstall: my APN is still called internet as by default, and SFOS browser works fine), but I allow myself to think this issue is somehow more related to SIM cards rather than providers, because 1) the issue was not there before the card change, and 2) other users seem to have experienced similar troubles.
I am attaching here the logs* I got through Ofono Logger. I tried to connect via Firefox to either fast.com (or example.com), first while connected with wifi, then again after turning wifi off, only with mobile data. I hope they help somehow.
*Yes, I will obviously provide the key “to whom it may concern”, if case may be.
Oh, BTW, if I decide to select the mobile network manually, I can only connect to Iliad 50, but not Iliad 88 which shows up white (not greyed out), but replies with “denied”.