Oh huh! I hadn't realised that it *IS* possible to have an additional hashtag search column without actually following it. (Following the tag would clutter your normal Home timeline.) Do not click Follow for the tag but instead open Settings for the column and Pin it, then Settings again to add other tags if you want. An example I recorded:

#hashtag #search #mastodon #timeline #tutorial #AdvancedView #MastodonSearch #HashtagSearch #HashtagFollow #ColumnView #PinColumns