You can use DepotDownloader to downpatch the game to an older update, as a recent update made the skills much slower to level up. I won't be going into detail as to how to use DepotDownloader here as there are plenty of tutorials on Youtube on how to use it, so I'll just give important information specific to this game.

• App ID : 606490
• Depot ID : 606491
• Manifest ID : 2503404710774673161 (version from 4 July 2018)

After deleting the new files, paste the old files and rename the exe and add spaces (DuckLifeSpace to Duck Life Space) and do the same with the data folder (DuckLifeSpace_Data to Duck Life Space_Data). (credits to @Creepiumgamer, I copy-pasted this sentence from him on Discord lol)