I would not call this approach a best practice, though some have taken this approach. There are 20-30k monitoring conditions in a typical SCOM instance. Turning everything off is not easy. This is not approach that I would recommend. Event if you could turn it all off, it is impossible to know what to turn back on. How do you know what will fire in your environment before collecting alert data? What you will see is 200-300 unique alerts per year out of the box. With a reasonable tuning effort you can prune this down to 80-100 unique alerts. I disable alerts that are clearly problematic. Any remaining non-actionable alerts are set to informational. Then I hide informational from the main alert views and notifications. This keeps that data alive. Making it easier to make tuning decisions without the fear or making a mistake. That said there is a toll from Cookdown that can help if needed:
https://learn.microsoft.com/en-us/answers/questions/706545/scom-2019-turn-off-all-alerts.html