For some weeks, as a workaround for the bad LTE connectivity, I've been carrying a sensibly small and light mobile LTE router (TP-Link M3750) fitted with a second SIM card from my mobile provider, taking from the same data quota that the phone itself would use. For the time being, this workaround provides good internet access when I'm not at home, also while driving in my car, for both the phone and the devices for which I would otherwise use the phone as an access point like my laptop.
(Too bad that while it takes a Micro SD card, too, this is limited to 32 GB; otherwise I could store my