a pity. works just fine here for years …
I declare my iMac as the “server” by saying ‘enable incoming Bonjour requests’. On iPad and iPhone I DO NOT turn on (via empty checkbox) ‘accept incoming Bonjour requests’ and I add a ‘local network’ location and pick the iMac and select databases. when the portable machines are connected via WiFi to the ‘local network’ (at my global HQ), it just works. And quick.
I also have all devices running DEVONthink or DEVONthink ToGo to sync via Dropbox. that useful for “catch-up” when I’m travelling, but of course I’m not at the moment and probably won’t for a while.
Out of DEVONthink’s control, but using iCloud to sync the folders in iCloud that DEVONthink creates just don’t sync fast enough to meet needs. There are also indications of unreliability if the iCloud folders change while syncing. So, don’t depend on iCloud and don’t expect that you can bend iCloud to your will meet your needs. If you need to try, best to discuss with Apple to make their product more robust and fix your issues.