With syncthing or the similar Resilio you can sync folders between your computers. This works best if you also install it on a NAS so as intermediate storage constantly available.
Nextcloud can do this also but adds a lot of other functionality. This is a cloud. You can access your files from any device. You can upload photos from your mobile. You can share files. You can create and edit documents. Play music. Show your photos. There are many apps adding further functionality. And you can install Nextcloud on your NAS at home or any VPS service