How to enable HiDPI support on Zoom.us linux client?

An answer that does not require changing common files that may be changed by future installs:

Zoom currently creates a file named zoomus.conf under your .config folder in the user's home folder.

One of the settings is ScaleFactor, set to 1 by default. Set this to 2, and next time you start the application it will have appropriate-sized visuals.

Recently I faced the opposite problem on Ubuntu 20.04 with Zoom 5.1.412382.0614: the UI was zoomed in and everything was too big.

The scaleFactor setting in the zoomus.conf file mentioned in the accepted answer was set to 1. However, changing the autoScale parameter to false solved the issue.

And as mentioned in the comments to this answer (thanks everyone!) it may be necessary to also set useSystemTheme=true so the autoScale parameter setting is respected.

The scale is set in an environment variable QT_DEVICE_PIXEL_RATIO.

You can add it to the desktop file in /usr/share/applications/Zoom.desktop by changing the Exec line to Exec=env QT_DEVICE_PIXEL_RATIO=2 /usr/bin/zoom %U

Or add export QT_DEVICE_PIXEL_RATIO=2 to you profile script

Source: zoom.us support