Smart Groups (both global and those specific to a database) created in 2.2 (or earlier) should still be present under 2.3.
Tags are active in 2.3. What is it that appears to be missing? The tag bar? Tags group? Something else?
Look at File > Database Properties for any database. If the option Exclude Groups from Tagging is checked, then it is not possible to include a group for tagging, and you will not see that option in the contextual (right-click) menu. If Exclude Groups from Tagging is not checked, then you’ll be able to decide on a group-by-group basis by using the contextual menu. Any include/exclude settings you had on this before moving to 2.3 should work as previously as soon as you uncheck the Exclude Groups from Tagging option in Database Properties.