If you get S20FE around 45k then surely go for it, and if you are a kind of rough user then also go for S20FE as it has polycarbonate back(good quality) which will not break if it falls or else if you have no budget problem then definitely S20+ is better in each and every aspect. If you want great performance then go for Galaxy S10lite(snapdragon 855)
If you can afford to spend the money on S20+ there is no reason to look at S20 FE. The only advantage I can see of FE over Plus is even though battery is same, FE has a lower resolution display and so should last you longer than the other. Or maybe if you like flat screens better than curved ones, you can go for S20 FE. The main advantage of S20 FE is the 10k or so money you save over the Plus model without losing much of the features.
obviously both have their strengths and weaknesses but I say its s20Fe which has better camera because of 3x optical zoom rather than croping a high resolution picture in case of s30 plus. But only thing I saw is the difference in shutter speed when on auto mode is little slower in Fe compared to s20 plus apart from it FE goes neck on neck..