How big do you set your canvas for maximal print quality? Suppose you want poster sized prints, or bigger.
Use Clip studio paints anti-aliasing scale upres and remember to put in 300 dpi. CMYK mode.
Then paint over parts in smaller canvases and patch it all together at the end. Or get a badass computer and paint in 20000x15000.
>>3137709
10,000px at 300pdi
>>3137709
The best upscale algorithm I have found is in a free app called "A Sharper Scaling". It produces way better results than Photoshop's own IMO.