Quick Answer
You can get the free Can 'Em All demo on Steam and manually copy its save into the full game. Back up both save.sav files before replacing the full game's file with your demo file. This Windows method worked for one player; you have no official transfer guarantee.
Where can you play the demo?
You can download the demo from the full game's Steam store page.
Find the demo download
Open the store page and find Download Can 'Em All Demo.
Download the demo
Select Download. You can also use Add to Library.
For more store information, see the Can 'Em All Steam page.
How do you move your demo save into the full game?
You replace the full game's save.sav with the demo's save.sav, after backing up both files.
You are following a single player's Windows transfer method. Keep separate backups of both saves before replacing anything. Replacing the full game's file overwrites that save.
Open LocalLow
Press Win+R, enter the following path, then press Enter:
%USERPROFILE%\AppData\LocalLow
Find both game folders
Find LuisDev, then open Can 'Em All Demo and Can 'Em All inside it.
%USERPROFILE%\AppData\LocalLow\LuisDev\Can 'Em All Demo
%USERPROFILE%\AppData\LocalLow\LuisDev\Can 'Em All
Back up both saves
Find save.sav in each folder. Copy both files somewhere else as backups. Keep them separate so you can tell them apart.
Replace the full-game save
Copy save.sav from the demo folder into the full-game folder, replacing the full game's save.sav.
What if you cannot find the save files?
You may be unable to locate the files; another player reported this, without a confirmed fix.
That report does not establish that the transfer method fails. Further guidance for missing files is still being added.
Before you buy, see on Steam Deck and the walkthrough.
FAQ
Yes. It's a free download on the full game's Steam store page.
Look under %USERPROFILE%\AppData\LocalLow\LuisDev. The demo and full-game folders each contain save.sav.
Copy the demo's save.sav into the full game's folder. Back up both original files before replacing the full-game save.
No official transfer guarantee is available. One player reported success with this manual Windows method.