KeePassXC doesn’t do any cloud syncing stuff. If you want your vault to be available on multiple devices, it’s up to you how to achieve that (e.g. by putting the vault database file inside dropbox/gdrive/nextcloud, etc). Some people prefer this approach because they don’t trust centralized vault services.

1Password and BitWarden are competitors and offer largely similar services (e.g. syncing your vault across all devices you own). BitWarden paid service is cheaper though, so it’s more popular. Note that bitwarden free account is already good enough, the paid service offers some convenient features which actually pretty nice to have though, such as storing TOTP data in your vault.

VaultWarden is an alternative implementation of bitwarden server. If you’re into self-hosting and want to host bitwarden vault on your own server, you can install it in your own server. It implements almost all bitwarden features, even those that only available in the highest subscription tier.