Now that Solspace Importer is a legacy product, what is the recommended method to import tags into my new EE3 installation? The rest of the entries are imported (using DataGrab and XML), so I can use the titles and URLs as keys for the import; but I cannot get multiple tags to import just using DataGrab. I tried separating the tags with commas, but when that imported in and was associated with the entry, what I got was one tag with commas in it rather than five separate tags on the entry.
If you are running an upgrade from v2 to v3, Tag will take care of all that when you upgrade the module. https://solspace.com/expressionengine/tag/docs/updates/
compare the table schema for tag 2 vs 3. they may be identical and you can just copy over the tables. Don't quote me on that.
On other upgrades ( for other modules) I have deleted the row in the modules table for the addon. Copy over all your tag tables, upload the tag files for v3, put the data back in the modules table (from your v2 install) and then just run the module update. It's a work around I know, but saves having to try and export and then import and really doesn't take very long. I can confirm it works.