Just follow the instructions In my link, please.
Per the link.
”If you have a newer iDevice, install the newer version of the app to your newer iDevice first.
Then, back on your iPad, you can try to download the latest app from the iOS App Store and if the developer/s has/have left an older, compatible version of their app/s on Apple's app servers, then you will receive a small window pop-up prompt that states that there is an older version of the app that is compatible with your device.. Would you like to download this version now.
Tap the OK button just below the prompt to start the downloading of the older app version to your iPad.”
If you do not own a newer iDevice running a newer iOS.
If you have a computer with an older version of iTunes (version 12.6.5 or earlier ), you can try downloading the most recent versions/s of app/s, by accessing the iOS App Store, through iTunes, logging into the iOS App Store using your Apple ID and password, and then, download the recent version of the app/s you like to use on your iPad, to iTunes on your computer, FIRST.
Then, follow the instructions given above.
Using either procedures will get you to installing an older version of an app/s ( if still available ) onto your older iDevice.
Follow either instructions for your particular circumstances.
I am not going to give you another long, detailed, explanation of why these two procedures work.
Just follow my detailed instructions and you will end up with older versions of drawing apps for your older iPad.
Some of the better drawings ARE still available and still are supported under iOS 9.3.5.
I will try and compile a list of all the ones I still have and still get updates under iOS 9.3.5.
In the meantime, find sketching/drawing/painting apps you are interested in and try and my procedures for getting the older versions for your older iPad.
Good Luck to You!