Adding Gmail account to flatpak-based BlueMail app on Silverblue 37

Hi. I just found BlueMail in flathub (I already used this app on Android for quite some time). I am unable to add my Gmail account to it (my university Microsoft account went just fine). When I try the automatic option, it open my browser, I grant the required permissions and click continue. Then, nothing else happens. The app stays in the waiting phase. I suspected a permission issue but in flatseal I am not sure what to try. I tried a manual configuration but it failed too. No progress with the rpm version, so I stick with flatpak. I found several other issues with the app but this one is the only critical. I even checked my Google settings and BlueMail shows (at least for the Android flavor). Any ideas?

BlueMail is proprietary, closed-source software by Blix Inc. Please contact their support for program-specific bugs and settings.

Thanks. Yes, I know BlueMail is propietary and I intend to contact support. But so is Mailspring and other email apps I have tried on Linux and never found an issue like this. Since I am running Silverblue, I though there was a better chance to find assistance in the forum.

I found a solution.
After all hints from BlueMail support failed, I created an app password in my Gmail security account and then used the manual option to enter Gmail’s parameters, with the new app password. I’m now connected. It seems BlueMail for Linux is somewhat considered “insecure” enough by Google to allow it. No such an issue with the Android version at all.
I have used many email apps in Linux over the past two decades, from Balsa and Sylpheed to Evolution and Thunderbird. But I consider BlueMail the best email app for Linux right now, even though it has its issues. The rpm version did not even launch in Silverblue. But it has a modern look, somewhat similar to Geary, with several other unique features I love to use.

As an update, I went back (yet again) to Evolution. I was finally successful in connecting Evo to my university’s Exchange server, and recent UI changes made this app look a little bit more modern. BlueMail worked mostly well, but as in other closed-source apps for Linux, support is limited.