Would try to target communities that align with your target audience - Twitter, Subreddits, Facebook groups, or Discord. Can also promote more generally on some of these platforms or ProductHunt

Another method, guerilla testing, worked well in grad school. Go to a public place - a library, coffee shop, etc. Politely ask random people to test your project. The obvious downside is they may not fit your target audience, but it's a cheap and scrappy way to get some feedback.

Who's the target market? You should be able to find a persona of someone interested in it. Even if you built it for yourself, you should be able to make a persona that's a fragment of yourself, e.g. Jay who puts all his MMO stuff on spreadsheets and wants to migrate his sheets to a wiki.

Where do they hang out? That's probably a good place to start.

There's Uservoice and Mechanical Turk too, if you want a more general audience
1) build something which could be interesting to other people

2) make threshold to test the product and post feedback low (e. g. GitHub)

3) promote it on HN, reddit, producthunt...

4) people will test and some will report bugs / submit ideas etc.

Perhaps post some details here? As Show HN.
The fact that you don't realize you can post here, in this very community, really should give some pause.
What would you like to have tested? I might have time to provide some feedback.
Look out for Communities on Discord, telegram with whom your product aligns.
Sounds like Product Hunt to me.