Depending on your device, if your device is released in 2018, even an iTunes 12.6.5.3 (yes, the last version that has App Store support) can sync no problem. You just can’t use it to backup and install iOS anymore.
if your device is released On or after 2019, chances are you need iTunes 12.7 minimum, maybe even iTunes 12.8. However, you probably don't need macOS 11 and latest Xcode beta to just sync to your device running iOS 14 beta. iTunes support for your device seems to be tied with SoC generations rather than iOS version.