I would really like to be able to change the key from / to \ (or another custom key).

/ usually means "or" when typing out some form of list in a normal line of text - e.g., apples / bananas / oranges. So every time you press it, the slash command modal pops up.

Whereas \ is rarely used in text.

This was asked previously (https://feedback.clickup.com/feature-requests/p/change-slash-command-from-to) but was closed.