I thought others might find this fun, as this game has sorely lacked a dating and chemistry system.
The essential mods needed for this technique are:
SimDa Dating App from LittleMsSam https://littlemssam.tumblr.com/post/175413426238/simda-dating-app-simda-dating-app-can-help-you
Show/Search Sim Info Mod: https://modthesims.info/d/576053/show-search-sim-info-mod.html
Chemistry System: https://thepancake1.com/chemistry-system-latest-version/
I also use the attraction system from Wonderful Whims (the PG version of the mod which must not be named), but that's not essential to this move.
So, for an active Sim who is having a hard time finding the right match, you would first click the Sim and view their preferences in the chemistry system mod. Several trait preferences should be higher values in green. Pick the highest value, or even a couple of them. Next, use the "Search Sim Info" mod to search all Sims, and use key words to find Sims that have the values you are looking for. For example, I look for single Sims who have several of the traits my active Sim is looking for in a partner. This could look like "Spouse:no Trait:Active" or "Spouse: no Trait:kleptomaniac Trait:Romantic". You can put as many things as you want in this string, but the more you have, the less likely you will find someone that meets all the criteria. If you look up how to search with this mod, you could even search for Sims that have a certain career or amount of money. Choose one or two that look like they might be of interest to the Sim.
Next, go into the SimDa dating app and choose "Find a Specific Date" or something like that (it's the top option in the list) and find the Sim that has the matching criteria you wanted.
This is a little cheaty-but the way I look at it is that it's actually a pretty good simulation of how online dating works. People post on their dating profiles and you either like how they describe themself and how they look, or you don't. I also use the WW attraction system, so once they meet on the date there is no telling whether that will click or not, just like in real life.
I've been having so much fun having my Sims go online dating in this way!
My username has been my internet handle for over 20 years since I was 16 and refers to when I had a crush on a very tall boy. I intend absolutely no violence toward beautiful giraffes.