Show teasers from both content type and Users together in a view I would like to be able to create a page to show teasers from content created with a certain content type, say "Company" together with teasers from Users content.

Until now, I just managed to create either a view to show the teasers of the Company content type, OR the teasers of the Users. But not both.
When I add a relation, I can use fields of both in the same block, but I would like to show a page with separate blocks of both companies and users together.

How should I do such a thing, if even possible?
Since you say that you would like to show a page with separate blocks of companies and users, there's no need to do this all in the same View.

Create two different Views with Block displays. One for the teasers of Company content type, one for the teasers of the Users. (You have done this much already.)

Then, place both of those Blocks in theme regions on the same page, and they should both appear ... together, but separately.