@angeloears Can you please try something for me? Please create a separate new room area with a good amount of space in it, surfaces for the roomie to lay their junk (if not they will be unhappy, as they come with junk and usually a bedside lamp and at least one plant to put on a surface, etc.) and a bed. Then please try to take down the ad for roommates. Confirm that every sim in the household is assigned a bed successfully and that when you hover over the beds you see these bed assignments are set (you should see an image on hover as to who is assigned the bed).
Also, if you have any pets you should have an extra bed somewhere on the lot for each pet that's not assigned to anyone - you can delete this bed after you get the new roomie. I found in my game that I could have up to 8 sims (including pets and servo(s)) and a butler and can still add up to 2 roomies (for a potential capacity in the home of 10 with 8 being household members, plus one butler).
Anyway, then please confirm that you can place the ad again and then place a new ad. It usually takes at least a day for roomies to show up at my lot, and sometimes it seems to be triggered by saving, going to manage world, then re-entering the lot during the day and after the ad has been up for a day or so. Also, is your front door unlocked? I would unlock it while looking for roomies. When you return to the lot don'e be surprised if there are one or more roaming around your home. You can confirm they are 'Potential Roommates' by hovering over them.
Please make sure your game is updated.
Also, do you have any Mods or CC? If you are having issues getting the roommate function to work properly I would try moving the Mods folder to your desktop and delete the localthumbnailcache.package file, plus delete any other folder in the "The Sims 4” folder with the word 'cache' in the title. If this fixes the situation you can re-add your Mods/CC one at a time to see if one was causing the issue.
Let us know how it goes!