Just heard about Jellyfin today and it sounds awesome so I had to give it a go.
I downloaded and installed jellyfin_v10.4.3-x64.exe and installed it on a windows server box.
Browsed to the URL and made a user. Go to add media. I choose the drive where my media lives.
I choose the first subfolder and got a list of more folders. When I click on the next subfolder the ‘picker’ for lack of a better term goes away and then the box named Folder is left blank and outlined in red.
I have also tried to manually enter the path using the drive letter all the way down to the folder containing my media. Same thing each time.