1) Where do people that have use for your app hang-out or post about the problem that your app solves? Are there any online forums or subreddits or facebook groups where your target audience is? If so, I would join these communities and when someone has a problem that your product solves, I'd help them in the comments and point to your product. Many groups are (for a good reason) hostile to adposts, so your best bet would be to spend time and engage with the community as opposed to going for direct adposts immediately.

2) Post on LinkedIn (consistently) using keywords / hashtags that target your customer base. Use infographics or tutorials of your product to showcase how it solves a problem. I know LinkedIn can be a pain, but imho it has one of the best organic reaches of any big social media platform and it's free (apart from the time it takes to write and post).

If you hope to get customers - You're thinking about it wrong. First, the typical buyer doesn't trawl a "SaaS Apps" list site looking for services they need. Second, even when you list on a site like Product Hunt, the chances are low that any given visitor that sees your site the day it's promoted also needs your service. Instead, think about what search terms someone might use on Google when they have (or are about to have) the problem your SaaS app solves. Try and write the best answer on the web for those searches.

If you hope to get feedback - Again, probably thinking about it wrong. I'd try finding people who A.) You don't know and B.) Are uniquely qualified to give feedback on your service, and get in touch with them, try and offer something of value to them in exchange for feedback.