@aral I finally found the time to report it (https://forum.affinity.serif.com/index.php?/topic/226595-unexpected-network-connection-accessing-bookmarks-and-reading-list-entries/), here’s the response by a user marked as “staff”:
“From speaking to the Dev team, this will be Apple components doing their own checks. Affinity itself can't and doesn't read you browser bookmarks or reading list. This has also been reported for other apps as well, one of those reports is here (https://community.bitwarden.com/t/little-snitch-reports-many-connections-45-on-mac-desktop-client/75054/2).”
Of course I cannot verify this but it sounds reasonable.