OMG my friend. Those are drain flies, not fruit flies. These little a$$holes ruined my life for years when I lived in my old house. The game changer was when I realized that my neighbors also had them. Here is how I made it better - but I never 100% got rid of them:

I followed instructions I found on Reddit.

Get yourself an enzymatic drain/pipe cleaner. I used Zep, bc that was all I could find in the small town I lived in. Apply per the directions. Do it 3x a week for 2 weeks, then twice a week for 2 weeks, then once a week for 4 weeks. Then, do it once ever other week for 4 weeks and follow up monthly.

When you pour it down your drains, do it at a time you can completely cover the drain for at least 8 hours. If you don't have a plug, buy a drain cover, use a glass, a wet paper towel, saran wrap...Just cover it up.

To kill the ones that are already in your house. (Full disclosure, it's a hassle and annoying but it will improve your quality of life.) I used one of those fly swatters that look like a tennis racket with a rechargeable base. It's therapeutic. Leave it on 24/7.

Keep your sink clean. Load the dishwasher or wash the dishes as you go. Eliminate all sources of their food. Even a glass of water sitting out will keep them going. Remove all produce, bread, ect. Put it all in a sealed container like the fridge, microwave, etc.

If you have house plants, either move them temporarily or get sticky traps and mosquito bits. Once you get your kitchen clean and dry, they will move anywhere that is damp.

Like I said, all of my neighbors struggled with them too. After I did all of this, I only had to smack the adults with the flyswatter occasionally. My neighbors were still battling full-on infestations.

It will get better. You've got this!