Hello,
Would it be possible to make Anki save a backup on disk before each sync? Today I clicked “download” instead of “upload” by mistake and lost one day of work. The last backup I have on disk was made yesterday, when I closed the program.
Thank you
That would be very expensive, take time… depending on the amount of decks.
Backup on sync was the default behaviour a couple of versions ago and I, too, relied on that behaviour. I’d love to have it back again, even as a customizable option, as it is always good to have another backup when you sync. For me, syncing is a habit, but switching the user profile, which does initiate a backup even with the current version, is not so much of a habit, while editing and learning. So I see your point. 
As far as I know, Anki does make a backup when you click Download. There was a bug in some versions before 2.1.40 that prevented that though. Are you using a version older than 2.1.40? If so, I recommend upgrading.
I did the same its my first time using this platform and trying to sync and I choose to download and lost all of today’s work. can I do anything to fix this?
Check backups if you’re using a recent Anki version. See Anki Manual
Ok i found my deck how do I save it now to my profile and not lose it?
If you mean you found the backup file you want to restore, then just open it and it will replace your current collection as explained in the manual.
Right now I’m using 2.1.43 but when I posted here could have been older… Thanks for letting me know.
Anyway, I learned to always double-check before clicking on a sync. Very useful skill, in everyday life and work environments as well 