By "single payer" do you mean the European model of "socialized" healthcare? That may be necessary (I don't know) but it's clearly not enough.
I'm in France, and I hear the exact same complaints from physicians here [0], and the hospitals seem to be in terrible shape. People quitting or being on leave, hence understaffing, so more people quitting because of burnout, etc.
[0] Basically, the gist is that for some time, hospitals have been run "like an enterprise", seeking (cash) efficiency above all. There was absolutely no slack in the system, so when COVID hit, medical professionals ended up in a terrible situation. This situation has not subsided even after the epidemic became less of an issue.