What do you do with book series that does not have matching covers? Do you buy paperback editions of those books or make alternate covers?

The covers don't matter to me. The story/writing does.

I rather like having all different looking books. Why would I want them to all look the same? That's kind of boring.

As for different covers............yes, I collect Clive Cussler books, and various editions, alll have varying cover art.

I hate when I find a better cover art than the one I have.

It's nice to have matching covers but I would never make alternate covers myself.

Why would it matter? I only care about the story, not about the cover.

Wouldn't bother me and I definitely wouldn't waste money making them look the same.

No. (Why would I?)

It would bother me, but I would live with it.

I relish an addition to up-beat ordinary bound covers.
Feel free to be seen as entirely plain and simple.

It wouldn't bother me at all. I suspect it wouldn't bother most book readers before bookstagram or booktube.

I turn the backs of the books to the wall.