How do you validate an idea?

I recently got fired from a job as a software engineer at one of the FAANG companies. I will take a break from any "9 to 5"s for the next 6 months and I want to take advantage of this time to try to create a business, most likely a SaaS.My idea is to create a service to help investors manage their portfolios. The idea evolved from a need that I personally have - I'm currently tracking my portfolio in an excel spreadsheet.From talking to other entrepreneurs I heard that it's a good practice to first try to validate the idea before actually investing effort in implementing it, which makes a lot of sense. They usually recommend to ask around in communities of potential customers. In my case, one such community would be the /r/Investing sub, or maybe /r/personalfinance. But I see that all these subreddits have a rule of "no self promotion", including this one. I'm a frequent reader of these subreddits, so I don't want to get banned for breaking the rules. Other non-reddit communities (e.g. Forums) have similar no self-promotion rules.So my question is: how do you validate your ideas with potential customers without making it look like spam or self-promotion? see hubwealthy.com/wealthy