The CSS file isn’t rendered inline in the header when you use the Custom CSS options in Theme Settings.
If you are trying to ask anything else then provide a relevant screenshot of the specific area with some explanation to check it myself and help you out accordingly.
The PageSpeed Insights tool from Google showed me there is unused CSS which creates render-blocking and slowing the site and this worries me to resolve it.
Attaching in private area details to see what I mean.
I saw the screenshot you attached. As it can be clearly seen that the CSS you mentioning is in the litespeed cache folder not related to our theme. You can try deleting the files from the folder.
No, it’s not dangerous to delete the files or the complete cache folder. The files stored in the cache folder are used by the cache plugin etc. As in your case the folder is for litespeed cache. You can download it before deleting if you want.