latex – Texstudio "package.sty not found" with Texlive on new linux 19.1

The first time I ask a question here. I am totally new with Linux, I just installed Mint 19.1 on my laptop 2 weeks ago.

I've installed TexLive and TexStudio. All packages are downloaded to / usr / local / texlive / 2018 / texmf-dist / tex / latex. But whatever I try, I always have the same problem:
TexStudio tells me that "dsfont.sty file not found. Usepackage".
I'm using it as an example, but it seems like it's the same for other packages I'm using.

I know that similar questions have been asked on the Internet, but despite testing the entire proposed solution, my problem is still there.
(I've updated the packages with tlmgr, I've defined the path directly in advanced texstudio options …)

I'm a bit desperate …
Sorry for my poor English.
Thanks for the help.