Although the crash issue has been fixed in the latest version 1.20.1, the data packet has become invalid

What do you mean? What 'data packet'?

It's the data pack for changing the improvement formula, the one downloaded from the webpage, from Nether Star to Cobblestone

Yes, salvaging recipe is missing slots entry. It's there just as reminder of that you should also adjust it when you modify modifier recipe.

Slots entry in salveging recipe is mandatory and cannot be set to 0. I decided to not put it there as salveging recipe in not necessary for given cobblestone example. If I set correct value (e.g. 1) people could get 1 free slot every time they remove modifier from tool. As it is now salveging recipe is not loading, but modifier recipe is working just fine.

Either way error message is clear and simple, so if you need it you can easly fix it for yourself.