@temijun
Hi temijun!
First: I'm no expert so I give you an uneducated opinion. If I'm wrong hopefully someone else is correcting me.
In your logs:
1. Ignore everything with "E QCOM PowerHAL: Failed to acquire lock." I get the same errors constantly.
2. For me it seems that the LTE modem is working. Since you cleared private DNS in settings it is T mobile that sends an ip address and a domain name for a private DNS server (DnsAddresses: [fd00:976a::9,fd00:976a::10,] UsePrivateDns: true PrivateDnsServerName: 1dot1dot1dot1.cloudflare-dns.com)
3. Obviously every communication is with IPv6. Which is totally ok but for a normal human being hard to read. That's the first difference to my setup. My ISP still uses IPv4. We just have to keep that in mind when we dig deeper into the problem.
4. Netd is needed for DNS and I don't like the line
"07-04 10:27:10.489 360 455 E Netd : Error adding route ::/0 -> (null) (null) to table 1003: No such device"
Summary: physical connection with modem works. Problem is in software code. Somewhere something is blocked or throws an error. Most likely in ip6tables (my iptables for IPv4 work).
So what would I do (remember I'm no expert)?
0. (just checking): When you flashed LineageOS 16 - did you wipe cache / davlik / data / system?
Iptables-rules get appended. I want to rule out that there is no leftover from a dirty flash over LOS 14. If you haven't done a complete wipe before please reinstall LOS 16 in a clean environment.
1. I don't know if it helps but it is easily done:
Activate the Terminal in developer settings. (If you don't have them visible - you need to tap 7 times on the build line in settings - system info - use google for help).
Open terminal app in app drawer and type
ping 8.8.8.8
(Enter)
This calls Google Nameserver with IPv4
A) If you get an answer like
64 bytes from 8.8.8.8: ...... time = xx ms
the server is reachable (Hints in my opinion to a blocked port 53 or disabled / restricted netd). Unfortunately I don't know if it is at all possible to ping IPv6 addresses like the one from your t-mobile DNS [fd00:976a::9]. Maybe google can help you.
B) Or the answer is:
"Network is unreachable."
Then a lot more is blocked.
As a next step for testing you would have to dig deep into OS areas like iptables. There is definitely something wrong with your rules. That leaves the question: Is that only in your specific setup or is that a general problem with this LOS build?
I never went as deep as that into the bare operating system. What I can only offer you is help with a quirky test setup and only if 1. A) above is working and you can reach Google DNS. Then I could help you force DNS with IPv4 and general IPv4 traffic. But It would require you to install AFwall as firewall after rooting your device. Because that is the only way I know how to manipulate iptables rules. There is an option to add custon rules in a file. Not the most elegant way but for testing purposes... And if the provisionary fix works - you could keep it.
Or you invest hours reading the internet about iptables (and most likely are non the wiser)...
Or maybe someone else jumps in to help with your problem
One step at a time.
Concerning your USB connection problem:
In developer settings there is an option to set the connection always to MTP. Try to use that if you are not concerned about a possible security issue.
Good luck.
edit: Since your USB connection is also behaving strangely - maybe you want to do a clean reinstall in any case?
