Chromium PWAs: how to open links with system link handler (default browser)?

I use Chromium only for PWAs like the Element Web UI of my server, to avoid Electron.

Now I have a different browser set as default in my system.

Firefox of course integrates perfectly and uses the "system link handler" to open links.

I want to make Chromium use this link handler, to open every clicked link not in the same browser but send it to my system link handler and thus open in my default browser.

I already set #enable-user-link-capturing-pwa Disabled in chrome://flags. The addon "Open in Firefox Browser" seems to be broken.

I dont know how manifest v3 interferes with that ability of addons to hook into the link handling of the browser.

Btw Chromium has not a single "portal" setting in the flags, but uses the filepicker portal by default.