I know that this is a slightly older thread, but the following might be helpful if you want to avoid ADE 4.5 and the "hardened" DRM.
You can also run the 32-bit windows version of the old Adobe Digital Editions 2.0x under Big Sur (tested by me) or other 64-bit OSX versions (Catalina and possibly Monterey) by running a special version of wine that runs 32 bit apps.
First, I recommend backing up any existing OSX Documents/ADE folder as installing ADE 2.0x could overwrite it.
Download ADE 2.0x for Windows. It's easiest to find later if you put it on your Mac desktop.
Install homebrew from the terminal (OSX command line installation tool). Note that if you haven't already installed the XCode command line tools from the App Store, it may prompt you to do so.
Code:
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
Then install
this version of wine that runs 32-bit apps from the terminal:
Code:
brew install --cask --no-quarantine gcenx/wine/wine-crossover
and winetricks:
Code:
brew install winetricks
Then install these libraries required by ADE 2.0. You will need follow prompts to and hit enter/press ok a couple of times during the lengthy .NET installation.
Code:
winetricks corefonts dotnet35sp1
Start windows using winefile.
You can now install ADE 2.0 for Windows. Ideally, you have put the ADE installer file on your desktop so it is easy to find. Double click the file to install.
Authorize ADE 2.0 with your adobe login and password.
You can now double click an acsm file in winefile and it will open ADE 2.0 and download it to your Documents/ADE folder. Again, acsm files are easiest to find if they are on your mac desktop.
After you have downloaded the epub with ADE 2.0,you can read it there. Or you can import into Calibre using the DeDRM plugin as documented elsewhere. Note that you may have to extract your adobe keys if you haven't done so previously.
The drawback is that you will need to start winefile every time you want to run ADE 2.0, where installing ADE 4.5 is native to osx.