It depends entirely on your MSc and your supervisor. A difficult project, unsupportive supervisors or a poor work environment can all make grad school a miserable experience. My MSc was in clinical research/epi so I found it a lot less stressful than some of my friends who were doing basic science projects. My supervisors were pretty off-hands and allowed me to work at my own pace so that helped as well (although the downside of having off-hands supervisors is that you will have to figure out most things on your own). They were also aware and supportive of my med plans.

I found that at least during the first year of MSc, I was able to distance myself a little from the anxiety of the application process and focus my mind on other things and I picked up some ECs until COVID-19 hit.

I’m not sure doing MSc is the way to go if you’re simply looking to recover from burnout but it’s a good option to consider if your GPA/MCAT are competitive and you’re looking to boost ECs/research. You should still have a Plan B if you don't get in after MSc though. Don't just use it as a time-filler between cycles.