Since the support life of my OnePlus 8T's official ROM is about to end, I flashed Nameless OS, a Lineage OS based third party Android ROM, onto my phone. But after flashing the ROM, I found that my China Telecom SIM card cannot roam on the 4G network of local mobile service providers, only 2G or 3G work. Since the local providers are recently shutting down 2G and 3G networks, the roaming cellular signal strength is really bad. I experience a high latency on receiving or sending messages, nor can I use VoLTE to make calls normally. I tested other Lineage OS based third party ROMS, and experienced the same problem. After numerous attempts, I found that the problem seems to be with the phone's APN settings. I use the term seems to be because while changing APN settings fixed my problem,...