It's hard to recommend S20FE5G over S10Lite because performance difference is negligible. Battery life is also still pretty good and I got the phone on launch day. You do get a better camera, Qi charging and water resistance. Apart from that, you are essentially getting a pretty similar phone. I loved the phone though. It just feels better in hands even though size difference is very negligible (display is 0.2" smaller iirc). But the wifi issues were noticeable enough regularly so I decided not to keep the phone. It might get fixed in a software update.
Another thing to consider is that FE launched with Android 10 so both phones have same update schedule. Both would get Android 12 and 13. FE should get a few months more of security updates.
If you are happy with S10L, I would suggest waiting for a while. It's likely Samsung would keep the price of Fe low and the same deals would remain available frequently in coming months. By that time, it should be clear if Samsung would fix the issues many folks are facing. And we might end up getting the S21 FE sometime early next year. Which might turn out to be a better phone to upgrade to.