James Gasik
We don't talk about Pun-Pun
Read that part about Copying a spell again. "If it's of a level you can prepare" is the key.Technically RAW this is true in 2024 rules. You can prepare a spell as you have slots for it and you can copy it into your book as long as you can prepare it. Here is the relevant text:
Prepared Spells of Level 1+. You prepare the list of level 1+ spells that are available for you to cast with this feature. To do so, choose four spells from your spellbook. The chosen spells must be of a level for which you have spell slots.
Copying a Spell into the Book. When you find a level 1+ Wizard spell, you can copy it into your spellbook if it’s of a level you can prepare and if you have time to copy it. For each level of the spell, the transcription takes 2 hours and costs 50 GP. Afterward you can prepare the spell like the other spells in your spellbook.
So for example a Wizard 1/Cleric 19 has a 9th level spell slot. So she can prepare a 9th level spell if it is in her book. Since she can prepare a 9th level spell, if she finds or buys a scroll of Wish she can copy it into her book.
This is not RAI, but it is RAW.
Now, in the multiclassing section, you find:
Spells Prepared. You determine what spells you can prepare for each class individually, as if you were a single-classed member of that class. If you are a level 4 Ranger / level 3 Sorcerer, for example, you can prepare five level 1 Ranger spells, and you can prepare six Sorcerer spells of level 1 or 2 (as well as four Sorcerer cantrips).
So, if you were a Wizard 4/Druid 1, for example, you would have 3rd level spell slots, but you can only prepare spells as a Wiz 4 (1st or 2nd) or a Druid 1 (1st). Since you can't prepare 3rd level Wizard spells, you can't copy them into your book.