WebUSB android flashing works in stock Chromium but not Chrome

Hey,
I want to flash my android phone with a custom OS using flash.android.com and grapheneos.org/install/web which both use WebUSB.

However Chrome is the only Chromium-based browser (that I have tested) that does not seem to work for me.

I already made an issue regarding this at GrapheneOS.
See https://github.com/GrapheneOS/grapheneos.org/issues/890.

Does anybody know how one might troubleshoot this kind of stuff.
Because it just seems odd to me that it works everywhere else.

The report names flash.android.com and grapheneos.org/install/web, with a related GrapheneOS issue, but it identifies no repository file, test, or entry point. Start by reproducing the WebUSB failure in Chrome versus another Chromium-based browser and compare the browser or Flatpak environment; done would require an identified cause and a verified fix.

Written by the indexing model from the issue text.