There was some issues with Thunderbird snap.
I reported some, Ubuntu team (was @oSoMoN ?) solved them. As far as I can experience, I still see one snap-related bug remaining: including an attachment makes it unavailable to open it from composer window. Not a big deal.
So I understand the concern about Snap Store proprietary software, but the snap itself is not.
And for the first time my Ubuntu story since 2006, I keep the LTS version, since I can get updated apps in a very stable system:
chromium 91.0.4472.77 1608 latest/stable canonical✓ -
chromium-ffmpeg 0.1 17 latest/stable canonical✓ -
code 054a9295 65 latest/stable vscode✓ classic
core 16-2.50 11081 latest/stable canonical✓ core
core18 20210507 2066 latest/stable canonical✓ base
core20 20210429 1026 latest/stable canonical✓ base
firefox 89.0-1 543 latest/beta mozilla✓ -
foliate 2.6.3 1167 latest/stable johnfactotum -
gimp 2.10.24 372 latest/stable snapcrafters -
gnome-3-28-1804 3.28.0-19-g98f9e67.98f9e67 145 latest/stable canonical✓ -
gnome-3-34-1804 0+git.3556cb3 66 latest/stable canonical✓ -
gnome-3-38-2004 0+git.3d25b9b 39 latest/stable canonical✓ -
gtk-common-themes 0.1-52-gb92ac40 1515 latest/stable canonical✓ -
gtk2-common-themes 0.1 13 latest/stable canonical✓ -
inkscape 1.1-ce6663b3b7-2021-05-25 9090 latest/stable inkscape✓ -
kde-frameworks-5-core18 5.61.0 32 latest/stable kde✓ -
kde-frameworks-5-qt-5-15-core20 5.79.0 14 latest/stable kde✓ -
libreoffice 7.1.3.2 218 latest/stable canonical✓ -
marsshooter latest 221 latest/stable diddledan -
quadrapassel 3.38.1+git2.e19fe71 361 latest/stable canonical✓ -
shortwave 1.1.1 1 latest/stable alexmurray -
snap-store 3.38.0-62-g77ca0c1 538 latest/beta canonical✓ -
snapd 2.50 11841 latest/stable canonical✓ snapd
stellarium-daily v0.21.0 732 latest/stable t4saha -
supertuxkart 1.2 556 latest/stable diddledan -
thunderbird 78.10.2 126 latest/stable canonical✓ -
vlc 3.0.14 2288 latest/stable videolan✓ -
xournalpp 1.0.20-9-gea457c9fd1 48 latest/stable ken-vandine -
VLC is another topic-related app (v 3.0.9 in repos).
I don’t even mention the snaps that are not available as deb.