A few people (including myself) experienced this constant DC issue and apparently someone mentioned a solution to this.
I finally gave up a few hours ago and uninstalled, made sure to clear leftover registry keys and everything before reinstalling, and I haven't had a disconnect since (knock on wood). But before that I did the following things, in order:
Checked pso2.exe network activity while questing and while in lobby to see if any packet loss or hiccups were happening on my end before disconnect (0%, never saw any issues)
Reset my network stack in cmd and restart, disconnects did not improve
Turned off IPv6, to no avail
Finally wiped my install and redownloaded using Tweaker as before, which worked.
I hate that I'm recommending reinstallation of a ~90gb game, but if you're having this issue and the usual troubleshooting doesn't work for you, it might be time for the nuclear option.
You can try it if you want to. For me, I dc'ed even when I was still VC on discord with my alliance, so kinda obvious this is a PSO2 problem and it only happened after the recent update.