I recently updated my desktop Anki and in response to it asking to upgrade to V2 scheduling, I confirmed and then responded that I do not want to go back to V1 in the future.
However, I did not remember that I have an old android device which newer versions of ankidroid can not be installed on it, and now it can not be synced anymore.
How could I go back to the old scheduling, so my old device go back to the syncing cycle again?
You have to downgrade to a previous version to do that.
From Changes - Changes :
There is no option to downgrade to the V1 scheduler anymore, though you can still do so by downgrading to an older Anki version first.
Also be sure to read the notice at the top of the page:
After using the latest version, if you wish to open your collection with an earlier Anki release, please go to the File>Switch Profile menu item, and click on “Downgrade & Quit”. If you skip this step, you may get an error message when opening your collection in an older Anki version, and you will need to return to this version, downgrade, then try again.
Thanks. I could switch back.