Increased view density option
Coming from Gmail, I am used to having three options for display density- Default, Comfortable and Compact. In Proton, the compact option still leaves too much space both in the LH folder/tag pane, and in the email listing. I suggest adding another density option. Since Compact is already used, the choice of Default may need to be added and then increase the density on the two existing options.

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J. C. commented
I agree there is far too much whitespace between folders/labels in the left-hand column in Compact view.
This should be reduced in the EXISTING Compact setting (regardless of whether a 3rd view is added as the OP suggests), because at present the label/folder spacing in the Compact view is exactly the same as in Comfortable!
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Shaula commented
Also a google switcher who used their compact and misses it.