Apache Webserver is not recognizing new Content

Hi I am running Jellyfin on my filme.serverwolf.de domain. Last night I tried adding some Buttons to the Interface and it worked great, but at some point I replaced a file in the web Folder and now everything is broken. (Only login screen works, but that's NOT false code! I put back the old file)

Login for you= User: "guest", Password: "guest"

To understand what I did:

1. I used Samba to connect from my PC to the server with the following permissions:

smb.conf

[*(Censored)*]
path = /
    public = yes
    writeable = yes
;       browseable = yes
    valid users =  *(Censored)*
    force user = root
    force group = root
    create mask = 0770
    directory mask = 0771
    force create mode = 0660
    force directory mode = 0770

2. Then I edited a file locally and replaced the one in my website.

I changed the file permissions already because it wasn't the same as the other files.

Before I also failed to add my own logo and thought it might be the image type but now I realized any new file gets rejected. Thats why I guess it might be https related BUT when I connect via http I also have the same issue what keeps me guessing wrong I think. The server is running behind a reverse Proxy and I certified it with certbot --apache.

Chrome Inspect (LibraryMenu.js is the file I replaced)

PS: By the way, this is not a specific problem for this website. My other website running on this server has the same problem. Couldn't make the background show up... When I replaced the index.html file the page was not visible at all anymore and it is still not showing. Don't really know what to do but something about my configuration seems off.

I am pretty new and have no experience with webhosting, so please excuse me for my basic level of understanding :)

Thanks in advance for you help, Simon Wolf