As you said for, "after the crisis", so let's forget graphic card and let's keep budget of $420 in mind.
Going from R5 1600 to R7 3700X (about $300, I guess) is a very solid performance increase. I had 3700X and I can really recommend it.
Yes, Asrock B450 HDV R4.0 is very basic motherboard, but I'm sure it can run 3700X just fine. So you read this board is "very bad".. and that's the reason? But is served you well so far, didn't it?
I ask because Strix B450-F isn't considered as cheap board (your budget is limited) and your PC won't perform any faster if you swap B450 for B450. And finally, maybe you would wish to buy some nice & quiet CPU cooler too... or (bigger) SSD -which does increase performance.