the thing about jdownloader it does not grab url and transfer it immediately to download manager with extension like IDM does.

I use Java version of XDM and it work flawlessly on brave and firefox

as long you stayed away from Ubuntu GNOME made by canonical and stick to other Ubuntu derivatives like Kubuntu,Xubuntu etc. they are good and stable distros without forced snap (I know Thunderbird,Chromium and Firefox got snapped because of the backend side. So, this is not their fault and you can switch to other ppas to mitigate this) and their software center app like discover still prioritise apt and flatpak.

Kubuntu and other Ubuntu derivatives are okay. they still use apt/flatpak on their software center