Thanks Kamil. I’ve migrated to SilverBlue 40 and I still face the issue with
gtk4-4.14.2-2.fc40.x86_64
xdg-desktop-portal-gnome-46.0-1.fc40.x86_64
Initial Memory usage for xdg-desktop-portal-gnome process was 38Mb.
I launched Brave and then I made a series of Save As/Ctrl-S calls (just firing the Dialog Box is sufficient to increase memory usage went to 109Mb , then 121Mb, 131Mb, 140Mb, 149Mb , 158Mb.
I hope the bug will be adressed soon / so far no reply to your comment in the bug report.