Can I use a meme I found for my business? Can I just it just for fun?
You can, but you're not technically allowed to. People do it all the time and they don't tend to get in trouble for it, so you're probably safe. But lawyers are in risk-mitigation so I would recommend you don't. I know. I'm a killjoy.
Is it possible to copyright something an AI draws or writes?
Not really. We're currently fighting about the extent of that "not really" right now.
How do I split revenue from IP with different owners?
It's actually the same answer regardless of what type of IP you're looking at - you have a contract and you follow what the contract says. Now, how do you come up with the system the contact spells out? Negotiation. Long, hopefully pleasant, negotiation.
What’s “transformative” and how can I tell if my changes count?
Copyright infringement is limited by a concept called fair use. A use of a copyrighted work is called “fair use” if it is technically a copyright infringement but the courts consider that the use should not really be regarded as an infringement. The fair-use defense generally measures 4 factors, of which one is “the purpose and character of the use, including whether such use is of a commercial nature”.
If the use is considered “transformative”, it can go a long way toward showing that the use is a fair use. Examples include parody or satire, where the use of the copyrighted work is to present a different or even an opposed message, or to make fun of the copyrighted work or its author. There is no bright-line test; it depends on whether courts feel the use is so different from the copyrighted work that the use should be allowed despite the copyright.
Can I copyright code or an app?
Yes. Copyright can cover a variety of things, including text, drawings, photographs, and code (including both source code and object code).
Recent rulings by the Copyright Office have said that AI-generated works are not copyrightable, so you might have to have written the code yourself. It is even possible to have a copyright in code that you maintain as a trade secret, so long as (a) you actually maintain the code as a secret. See the discussion of what is needed for something to be a trade secret.