How to connect a tablet as a second monitor for a macbook?

Question

macOS

I really need a second monitor for a macbook pro 13", but

• Compact, ideally within 13"
  
• HiDPI, i.e. retina
  

Judging by the online market, retina monitors of 20-22 inches are not currently on sale, and even 24" is unrealistic to find something with a small dot. The obvious solution is to connect a tablet. You need to work with a second editor / browser window in the coding process , 30 frames per second is enough.
What is the best software to do this? Is there any free software?
I found good reviews on duetdisplay (only ipad as a tablet) and on iDisplay (you can use both ipad and android).On Air Display, the reviews are rather bad, on a few chinese programs are really bad and their websites usually don't work, although the application is in the app store.
I would like to use a tablet on an android - it will come in handy in everyday life, but what else and why to do with an iPad, I could not think of. Those. I do not see an alternative to iDisplay, but I would like to be cheaper and generally have a choice.

Answer 1

in English with pictures will suit?
www.instructables.com/id/Tablet-Second-Monitor

Answer 2

> and even at 24" it's unrealistic to find something with a small dot
Dell P2415Q - why not?