remove the /portfolio-item/

Hi, I know, there’s a lot of topics with the same issue, and I do not lie or exaggerate, if I say that I have read them all.
This brings me upside down, the problem is that if I touch something in the Settings/Permalinks the page goes down, and the only way to restore it is to replace the htaccess file.
I have talked to my support server and they don’t give me any solution.
I can’t touch the permalinks without my page breaking
Can you tell me if it is possible to do something about it without editing the permalinks, or what can I do to modify the permalinks and prevent the htaccess from getting corrupted?
What I want to achieve for 182 portfolio files is that they look like from this:
https://rvarq.com/en/portfolio-item/3d-architectural-visualization-single-family-homes/
to this:
https://rvarq.com/en/3d-architectural-visualization-single-family-homes/
Anyway, I don’t quite understand, why a blog post does not end up being /Blog-post/ and why a portfolio does.
Has it been a mistake of mine from the first moment that I started to make portfolio items because the permalinks had not changed??
I hope there is a solution. Thanks