Do you use mostly Android apps?

No.

ls -1 /usr/share/applications/
Pacpac.desktop
csd.desktop
fingerterm.desktop
google-maps-geo-handler.desktop
harbour-2048.desktop
harbour-allradio2.desktop
harbour-android-offline.desktop
harbour-barcode.desktop
harbour-colortubes.desktop
harbour-crest.desktop
harbour-fbreader.desktop
harbour-file-browser.desktop
harbour-fivinarow.desktop
harbour-heebo.desktop
harbour-ieligimage.desktop
harbour-ieligweb.desktop
harbour-lonewolf.desktop
harbour-meecast.desktop
harbour-molecules.desktop
harbour-org.gpodder.sailfish.desktop
harbour-osmscout.desktop
harbour-ownkeepass.desktop
harbour-paketti.desktop
harbour-patience-deck.desktop
harbour-pipes.desktop
harbour-pure-maps-uri-handler.desktop
harbour-pure-maps.desktop
harbour-qml2048.desktop
harbour-sailpipe.desktop
harbour-sailtrix.desktop
harbour-sailtube-open-url.desktop
harbour-sailtube.desktop
harbour-sailtuner.desktop
harbour-seabass.desktop
harbour-sfos-forum-viewer.desktop
harbour-simplemahjong.desktop
harbour-sshazam.desktop
harbour-storeman.desktop
harbour-stppc.desktop
harbour-talefish.desktop
harbour-taot.desktop
harbour-wireshark.desktop
harbour-wordle.desktop
hosts-block-add-to-blacklist.desktop
hosts-block-add-to-whitelist.desktop
jolla-calculator.desktop
jolla-calendar.desktop
jolla-camera-lockscreen.desktop
jolla-camera-viewfinder.desktop
jolla-camera.desktop
jolla-clock.desktop
jolla-contacts.desktop
jolla-email.desktop
jolla-gallery.desktop
jolla-mediaplayer.desktop
jolla-messages.desktop
jolla-notes.desktop
jolla-settings.desktop
l2tp-import.desktop
mimeinfo.cache
new-mail.desktop
openconnect-import.desktop
openrepos-books.desktop
openstreetmap-geo-handler.desktop
org.kde.angelfish.desktop
ovpn-import.desktop
pptp-import.desktop
qCommand.desktop
qt-runner.desktop
quaeditor.desktop
retroarch.desktop
sailfish-archive.desktop
sailfish-audiorecorder.desktop
sailfish-browser.desktop
sailfish-captiveportal.desktop
sailfish-installationhandler.desktop
sailfish-office.desktop
sailfish-share.desktop
sailfish-tutorial.desktop
sailfishos-chum-gui.desktop
simkit.desktop
store-client.desktop
systemdatascope.desktop
uk.co.piggz.harbour-supersonik.desktop
voicecall-ui.desktop
vpnc-import.desktop
webcal-import.desktop
wheelmap-geo-handler.desktop
wireshark.desktop

None of those is Android (but not all are actual "apps").

I heard that the native browser is still some ancient Firefox fork.

I wouldn't say ancient; it's based on FF ESR98 or so's embedlite. But yeah, this is a topic of much discontent. Natively, it's relatively easy to install Angelfish (KDE) based on a much more timely webkit. Via Android appsupport many current browsers are available.

There is surprisingly little information about native apps anywhere, it strongly feels like they are mostly focusing on Android app compatibility.

It's one of their main selling points, but native apps are definitely abundant. There's the offical store, which does not have a browsable web frontend, and 2 unofficial stores: https://openrepos.net/ and https://sailfishos-chum.github.io/.

SailfishOS also has more closed source than I’d like to. Most often it does not end well.

I understand, but it has been going well since 2013. IMO the closed source thing is historical: they are the heirs of Nokia's Linux-based OSs. But slowly they are opensourcing parts of the OS.

Ultimately, this is a European company I can trust. The devs are active on the forum, too.

BTW, it is still and always will be possible to download & install SFOS on your own device, for €0.