Some positive news (expected, but always welcome), after 4.5.0.19 update (CLAT), after removing connman 1.32+git194.3 + the clat test repository, the phone can be used as hotspot with my IPv6-only operator. With plain vanilla 4.5.0.18 the hotspot did not work. CLAT is doing its work OK!
VPNs (Nord- and Proton-) still do not work (expected): one new ‘feature’ with those still useless VPN settings is that if you have the Advanced → Disable IPv6 Yes and you attempt to turn that VPN on, it is a kiss of death to the network connection, the VPN will not connect but the non-VPN network will not come back, either. If the setting remains Default, the VPN connects but has no effect whatsoever (ipleak dot net site). Same operator, different SIM, same network, a gulag phone: both (paid) VPNs work as expected on the aforementioned lP-leak test site. When needed, I can provide more logs, as I did above.
Thank you for this update!