Congratulations! You have proven your knowledge of adventuring!

[Niwashi]

If you can deal with splitting up when you're in a chatty mood or have specific questions you want to ask from when you're in the mood to focus on progressing your main character, you could get at least part-time access to the Novice Network back by just making a new alt character. The "New Adventurer" status is character specific, so even as you advance your main through Shadowbringers, your new alt could still qualify for NN.

It's far from ideal. Having to switch characters to reach your favorite chat channel means you can't be in it while you're waiting on a DF queue on your main, for instance, but maybe part time access would help tide you over until you can qualify to re-join as a mentor. Becoming a mentor is the better long term solution; it just takes quite a while to qualify for it.