I have a M1 Macbook too. I just updated to Sonoma 14.6.1 and downloaded using the Free Download button (for Apple Silicon Macs) at https://www.manager.io/download and got version 24.8.11.1812. I opened the .dmg file and dragged the red M to the applications folder.
I then opened Manager and as has been reported in the forum several times no longer saw any business files. The location of the files has changed to Manager.io in documents folder as can be seen bottom left from your screen, see screenshot:
From the discussion further below it was clear that I either had to look into:
/Users/**Yourusername**/Library/Application Support/Manager (for new users, although this now seems to have changed to the documents folder mentioned earlier).
Or if you are upgrading, the folder should be still the old
/Users/Yourusername/.local/share/Manager (my case as I already had business files)
I selected all files in the folder and moved them to the new location.