How do I sync tags between two Macs using Google Drive?

The tags you see in the Finder that are associated with a file/folder are stored as extended attributes of that file/folder.

There is an excellent article which goes into some details about the portability/syncability of these extended attributes. It suggests that Google Drive, amongst other cloud services, does not support the syncing of extended attributes, which is a pity. It lists three services which do support extended attributes, to varying extents, namely iCloud Drive (of course), Dropbox, and Resilio Sync.

I have personally found it effective when working with Google Drive to use workarounds to sync extended information. This includes different folder organization (e.g. red files in one folder, blue in other) or naming files differently. The exact way you'd do it is entirely based on the context of what you're trying to do, your goals, and whatever works for you.