My s21 ultra (exynos version) has been lagging for the past month. It happens when I open the phone. The refresh rate is like 10-30hz. And I've found that only by disabling Always On Fingerprint the problem goes away.
Today we got a software update and I was hopeful it would fix the problem. But it's still there. I'm very disappointed that I've paid 965$ for a top spec galaxy phone and facing this stupid issue.
Please suggest a fix if you have tried any successfully.