I only use the “M420 V” command for the bed visualizer plugin. (I just use it to visualize the bed, not to level it.
You’ll might need to use the release candidate of the plugin as with the glass in between you’re above 10mm of the zero point and it didn’t support double digit numbers until recently. (See For all who want level on glass - #31 by stefix and [BUG]: mesh data with points with more than single digits doesn't collect data. · Issue #352 · jneilliii/OctoPrint-BedLevelVisualizer · GitHub)
Your bed actually looks quite good. Even before the shimming. it was a fairly straight slope.
Did you tram your snapmaker? That might also help to get things more level. But right now I thinkg that looks pretty good. What’s the max deviation after the shimming?