Lightroom Classic CC uses a SQLite database called ‘the catalogue’ to store references to all images, metadata and edits. This database is meant to be used on one computer at a time.
To overcome these limitations, Adobe developed the Lightroom CC cloud based ecosystem. You basically have 3 options:
A: Sync the catalogue
Put the .lrcat file (and possibly the Smart Previews folder if you don’t synchronize all images) in some Dropbox or google drive. This is easy to setup, but you absolutely need to make sure that Lightroom is only opened on one machine at a time. Otherwise you risk corruption of the catalogue and loosing some or all of your edits.
B: Use mainly Lightroom Classic
With this approach, you need to declare one of your computers as main editing machine, and you need to do all imports there *. Then you enable sync with Lightroom CC (this works only for one catalogue at a time), and install the desktop version of Lightroom CC on your other machine. Keywords and color markings are not synchronized but all other edits are, so you can do editing on all your devices. This doesn’t eat up loud storage, as Lightroom Classic only uploads Smart Preview (Small editable images with reduced resolution). You can’t zoom in as far as with real raws but for most edits it should be fine.
* You can use a second catalogue while you're travelling, and then use the "import from other catalogue" option on your main machine. This way you can preserve all the edits, but you need to be careful with keywords and collections, to not pollute your main lrcat.
C: Use mainly Lightroom CC
You install Lightroom Classic on one machine, and use Lightroom CC for everything else, including importing of images. This costs cloud storage, but you can import less important images only to the desktop and just don’t sync them into the cloud. Again, Keywords and color markings won’t be synced between Cloud and Classic.
There is a lot of overlapping between option B and C, as they're depending on the same technology. You can use it e. g. to import and sync back images of your mobile phone back to your desktop computer.
