Why are Flatpaks that slow under openSUSE

Hey guys, I’ve recently switched fro Ubuntu 21.10 to Tumbleweed. First, I like it. It’s a great distro.
But tere is something whcih does really wonder me. Flatpaks start so much slower. First, the only apps that I’m running via Flatpak. There are PyCharm and Spotify on SUSE and it has been Xournal++ on Ubuntu which is available as RPM in SUSE fortunately.
When I was using Ubuntu I had tried snaps, of course. One property that everyone is aware of is how much they need to launch. I hated it and this is one of the key reasons why I just switched to SUSE.
Flatpaks started much faster. On Ubuntu, well.

One thing that remarked very soon is that SUSE is much faster than Ubuntu. Booting up is faster, launching apps is faster, everything is so wonderfully smooth.
But unfortunately, I noted that Flaptaks launch much slower. So, I’ve installed several Flatpaks such as Xournal++, Firefox, Thunderbird, LibreOffice, Chromium, Teams, etc. try that out.
And they all need a long time to launch as what I had been associating with snaps before.

Can anyone explain me why this is the case? What does Flatpak implementation do so different on SUSE than on Ubuntu?

It might be related to the version of flatpak Tumbleweed is using. Previously there was a similar issue related to the font cache which was supposedly fixed. I’m noticing the same thing on the first execution of apps but after that they seem to load much quicker. That might be disk cache. Some previous solutions suggest removing .local/share/flatpak/db/documents file but I can’t vouch for this.

Thank you, @FrankyU2 ! I did what you have wrote (removing ~/.local/share/flatpak/db/documents file) and it works on my system (Zorin OS Core 16.2). Thank you very much, I was losing hope, but removing ~/.local/share/flatpak/db/documents file did the trick and opening flatpak applications are in normal speed now.