Just got this DLC and am also experiencing this. The World is being hosted on an Xbox and if I try and Download & Join from my PC it gets to the exact spot that @Warriorman posted a picture of and then hangs. This is on Minecraft 1.20.41
EDIT 5 hours later: As I was comparing my screen with the one Warriorman posted, I noticed his showed 0/3 resource packs. Mine showed 0/4. After waiting an hour, I cancelled the download. When I tried a 2nd time, it showed 0/3, and again got stuck at the same spot (about 99% done). After waiting another 15 minutes, I cancelled the download and tried again. This time it was 0/2 resource packs, and it was able to download both successfully and I was able to join.
Same issue with Everbloom's Wizard School Roleplay. For me, the update button DOES update to 100%, then the package installs, but after installation, the "Update" button remains and I can't create a world use the world template, as it just instructs me to Update again. I've checked that there's plenty of free space, and I've also navigated to Storage and deleted the world template, which changes the button back to 'Download' instead of 'Update', but once I download it, it's the same loop, just telling me it still needs an update.
Also, I did try clearing the Marketplace cache as well, but this didn't help.
This happens on both Xbox (One S) and PC (Windows 10).