Have you tried unchecking the box to turn off “Use browser hardware acceleration” in battlenet settings? It’s at the bottom in settings menu. Also enable DLSS to balanced and change texture quality to high if you have it set to ultra. My PC can handle ultra but for some reason and I remember reading others state the same, the town environment does not like Ultra.
I was going mad with what I thought was lag. I believe it to be a combination of these things with poor optimization. Anyone can argue but I have not had any issues since I modified these 3 things.
Also, hit control R which will show FPS. Hit it again and it will display latency.