I haf some materials done in shops but when I use Solaris looks like doesn't like shops. But it shows all the ones from mat context. Is there any difference between the contexts?
Should I use one or the other?

From what I heard, shops are obsolete esp. for materials. So it's /mat or even /stage now.

I believe the mat context is more like vops, in that we have the ability to edit shaders at the top level. Whereas with shops, you need to dive inside to access the attributes. Shouldnt be a huge difference, but id suggest getting use to having your materials in the mat context

Houdini is a mess from an UX PoV right now. The desire to update the package so that it incorporates the latest tech combined with the need to keep the most backward compatibility possible, will get you there, I guess.