Yes, it’s unfortunate that the LineageOS support channels can be very unfriendly and not very supportive, particularly if you are running anything other than official LineageOS .
I do have a dual-SIM phone, but only for very limited testing. It doesn’t have even one SIM in it at the moment, and even if it did I don’t live anywhere that I could usefully test roaming.
And the limited time I have available for ‘work’ on custom ROMs is pretty much fully taken up with keeping the LineageOS for microG project ticking over, and providing occasional support in this and other forums. Sorry, and good luck in your attempts to get this stuff working!