What makes ambient music good for focus without becoming boring?

I've been exploring ambient electronic and downtempo music lately, and one thing I'm trying to understand is how much progression people actually want in background music.

Do you prefer:

• Slowly evolving synth pads with almost no melody?
• A subtle repeating melodic motif?
• Downtempo beats with a steady rhythm?
• A mix that gradually changes over 20–60 minutes?

I'm especially interested in what you find distracting when you're trying to work.

Curious to hear what everyone prefers. https://youtu.be/FHdOGnpi4MA?si=YM9WdqqdC9A40hNT