Syncing isn't a KeePassXC problem. The database is just a file. That may or may not make your life easier.

There are a few decent Android and iOS apps that work well. I use Nextcloud and WebDAV for access.

Not a setup I can recommend to just anybody though.

The mobile app is quite good, it works and gets out of your way. I use it on Android.

For syncing, I do it manually with rsync. Given the database is 1 file it's easy to move around. You can rsync / scp it over, use a USB cable, use cloud storage, etc..

I use a password manager in a "read many, write infrequently" way so I don't mind occasionally syncing it as needed.

I use keepassxc. I don’t sync mobile. My mobile device has an only the minimum subset of passwords I need saved on it.

These threads are always filled with keepass people who will tell you how great it is and not mention that you’re on your fucking own for you know Miner things like syncing or mobile use.

I’m sure it works for many people to Dropbox their vault around anytime they want to access something and manually handle copies and sync. I’m not nearly so naive as to think that has any degree of success outside tech bubbled people.