The culprit is missing mimetype in desktop-file. An example in Chromium need to add x-scheme-handler/zoommtg; to the /usr/share/applications/chromium-browser.desktop file. The same issue must be with other browsers like Firefox too.

su
nano /usr/share/applications/chromium-browser.desktop

… edit mimetype as

MimeType=text/html;text/xml;application/xhtml+xml;application/xml;application/vnd.mozilla.xul+xml;application/rss+xml;application/rdf+xml;image/gif;image/jpeg;image/png;x-scheme-handler/http;x-scheme-handler/https;x-scheme-handler/ftp;x-scheme-handler/chrome;video/webm;application/pdf;x-scheme-handler/zoommtg;

… edit, save and quit

Ctrl o
Ctrl x

… after editing run

update-desktop-database

Link to Zoom testpage https://zoom.us/test

For getting ZOOM to work better, it is good to take off denoise option from video settings. Also the right video driver must be loaded. An example PCLinuxOS in Compaq CQ61 requires i915 driver loaded.

inxi -Gx
Graphics:
Device-1: Intel Mobile 4 Series Integrated Graphics vendor: Hewlett-Packard
driver: i915 v: kernel arch: Gen-5 bus-ID: 00:02.0
Device-2: Silicon Motion - Taiwan (formerly Feiya ) HP Webcam-101
type: USB driver: uvcvideo bus-ID: 8-4:3
Display: server: X.org v: 1.21.1.8 driver: X: loaded: intel,v4l dri: i965
gpu: i915 resolution: 1366x768~60Hz
API: OpenGL v: 2.1 Mesa 23.1.4 renderer: Mesa Mobile Intel GM45 Express
(CTG) direct-render: Yes

That happens when /etc/modprobe.preload.d folder has a 20-i915 file which contens is

i915

BTW: I made this file by hand, because there had no the file.