r/fatfire - same thing as above but for people looking to have more than "just enough" to retire (multimillion, mostly full of high earners like SWE's, agents or successful entrepreneurs where this goal is somewhat realistic).

r/personalfinance & r/ukpersonalfinance - well rounded finance forum.

r/frugal - okayish for if you are in a really tough spot. If you are doing ok I generally don't recommend them because ultimately you are trading your time/health using most of the hacks from here.