KeePassXC does support passkeys. In Firefox I know you can turn off the thing where Firefox offers to save passwords. On Android KeepassDX (the mobile client) supports autofill
I'm glad you have something that works for you, but for me I would need something that is under a free software license, rather than closed source. Syncback offers a free product but doesn't use a free software license such as GPL.
Syncthing's setup isn't overly complex, but it can be a bit intimidating, but it is powerful and gives you plenty of options.