There is !personalfinance@sopuli.xyz, which would be somewhat related to personal tax. There is also a Lemmy instance dedicated to finance. I don’t recall it off the top of my head but the instance joined Cloudflare so I immediately abandoned it.

For the record, lemmy.ml is a terrible place to discuss tax or personal finance. The admins of that instance treat personal finance questions as spam and even go over the heads of moderators to censor such discussion because of their political baggage. IMO sopuli.xyz might be a good place to create an account and create finance communities.