I do not see the groups column both in my Softr view of the users tables AND the Airtable view of the users table.
First ensure your Users table is synced to Airtable:
After that, you can add the Groups column yourself as a multi-select field in Airtable, and then Softr will pick it up. Then, you can refer to it when creating a group:
Then click on “Logged in User’s” to see the list of columns in the Users table, and pick one: