I’ve had a change of luck with regards to the OS situation, which also is not directly related to installing an older version, but more circumventing the limitation on OS installation on apple hardware.
What I’m referring to is the Open Legacy Core Patcher, which has allowed me to upgrade my mac mini (late 2012) a few major versions (and I could go even further if I want to). Using OLCP I’m now able to run macos 12.x Monterey, and can use the newest Obsidian version available.
So to summarise your current options (not in any particular order) :
- You could downgrade from the links given in other post, but if possible be sure to turn off auto update first
- Upgrade your os to a supported version using Open Legacy Core Patcher, if your hardware is up for it
- Consider using Docker to bypass the os requirements
- Install Linux on your computer
I’m using 2), and it’s just working.