Just try running the Search For Orphans standard Query.

It lists everyone grouped by their Pool number.

Typically, your main family tree with all your relatives is in Pool number 1.

Anyone in a different Pool is totally unrelated to you either directly or by marriage.

So if you are not interested in such unrelated people then bulk delete them as follows.

Select them and use the cog Query Menu > Add Select Cell Records to Named List.

Then right-click the Named List and choose Delete Listed Records…

Mike Tate