For Illustrious: Diathornstyle, use tags like pony, recommend using Konanmix for better results
For Flux: digital illustration using diathornstyle
For Pony:

You can highresfix or rawdog it. I've gotten better results at 1024x1280 and 1152x1408.

Trained on Daithorn art, removed text/logo

Majority of their work isn't for everyone, their style is really great though!

High Res fix recommended!

Models that have "painted" look to them work best like dalcefo_painting