Hi all,
( In addition to my original question, there are more, I will describe them later like “Side Questions” )
Prelude:
Nextcloud installed on Docker via Apache Image in Windows 10.
After installation, I created an admin user and enabled the external storage application within Nextxloud.
I didn’t do anything special before and after!
Main Question:
I created a folder on another partition ( Docker installed on “C”, this Folder is on “D” ) on the computer that I want to add to Nextcloud, i.e. it uses this folder entirely for storage, sharing, etc…
How can I add this folder as “external storage”?
Side Question:
In the system settings, I currently see that I have ~250 GB of free space. I think this is what Docker allows (perhaps on the C partition). Perhaps this can somehow be reduced to the minimum possible (which is necessary for the operation of Nextcloud)?
Unfortunately, I’m not experienced in Linux and I couldn’t find a noob friendly step-by-step description / video for exactly this problem. If someone could help me here or even in a private message, or via messenger, I would appreciate it! ( even in exchange for a cup of coffee 
)
Thanks in advance for the help! 