When I will tag a photo - where i get the already tags to use for tagging? it is a disaster without because if you tag a lot of photos with time you use different words for same tag idea. with a lot time you generate much more tags you need and don't find all pictures because of different words ... or may be wrong writing... you see this in big picture databases a lot of people tagging. some spelling mistakes an a lot go pictures are lost because you never find back. with intelligent tagging like in Lightroom cc classic you can use easy already tags. but maybe I don't see a new way - won't believe there is no way ;-)
I am assuming that you are talking about the face taggings in Lightroom? Also, please let us know the version of Lightroom you are using now?
Also, when you tagging the unnamed people if you press "M" then it will show you all names which start with M.