Many thanks Binopy! It worked for me with a small change in the coding due to the following:

Calling Ext.GetStatEntries is deprecated; use Ext.Stats.GetStats instead.
See https://github.com/Norbyte/ositools/blob/master/Docs/ReleaseNotesv56.md for more info.

So, I used the following updated script instead:

for i,name in pairs(Ext.Stats.GetStats("ItemCombination")) do Osi.CharacterUnlockRecipe(CharacterGetHostCharacter(), name, 1) end

And all worked fine. Thank you!

1. Download "DivinityModManager_Latest.zip" at github.com/LaughingLeader-DOS2-Mods/DivinityModManager/releases
2. Extract it to wherever you like then run "DivinityModManager"
3. Click on "Settings" then "Open Preferrences"
4. Click "Script Extender" tab then turn on "Create Console"(just click on the box beside it), click the "Save" button at upper left corner of the window
5. Run D:OS2 game, "D:OS2 Script Extender Debug Console" will open too. Nevermind that for now and load up your save file in the game.
6. Once your save file finishes loading, go back to "D:OS2 Script Extender Debug Console" and press "Enter" once on your keyboard then copy & paste this in the console

for i,name in pairs(Ext.GetStatEntries("ItemCombination")) do Osi.CharacterUnlockRecipe(CharacterGetHostCharacter(), name, 1) end

then press "Enter" again to get it.

You can now disable "Create Console" in "DivinityModManager" to prevent it from running the console next time you run the game.