Is it normal to get a bsod once or twice a year?

Nope. My overclocked system 8700k running at 5ghz ram running at 4000mhz has never bsod even once over the past 3 years. Latest addition 3070ti running at 918mv 1965mhz +1000mhz memory also been running perfectly stable since the start of the year.

Sounds to me like your CPU undervolt is not 100% stable.

I will start by reverting any tweaks made to the CPU back to default and run everything on stock setting with ram on XMP enabled. If it bsod again then you can try fresh install windows. If it still bsod after that then it is likely a hardware issue. (Potentially bad ram)

or you can do it the other way round. Fresh install windows then revert CPU back to default settings.

Fresh install windows eliminate software as the cause of the BSOD. Reverting CPU back to default settings eliminate unstable uv/oc as the cause of the BSOD.