The Wizard includes the following feature:
Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a level for which you have spell slots and if you can spare the time to decipher and copy it.
Does this mean that a Wizard 1/Cleric 19 can copy any Wizard spell they find into their spellbook?
Is there anything preventing them from casting these spells?