IF you need older versions of apps for your older device, there are two ways of getting them.
The first and easiest way is to download the newest app to a newer iDevice, first.
Then go back to your older iDevice, download the newest version of the app, once again, 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 need apps for your older iDevice, if you have a computer with an older version of iTunes (version 12.6.4 or earlier ), you can try downloading the recent app/s, by accessing the iOS App Store, through iTunes, and then, download the recent version of the app/s you like to use on your older iDevice to iTunes on your computer, FIRST.
IF you own a computer with an older version of iTunes already on it, try using that version as an older iDevice does not need the latest iTunes version.
If you have a computer, but NO iTunes on it, here is a link to the older 12.6.3 version for download found in this Apple weblink.
Older versions of iTunes found here.
https://support.apple.com/downloads/itunes
iTunes 12.6.4 here.
https://support.apple.com/en-gb/HT208079
DO NOT download OR USE the latest version of iTunes (version 12.7.x) as there is no more support for saving apps in iTunes under the most recent versions.
If you have already downloaded the recent 12.7.x version of iTunes, NONE of what I have wriiten here in this post reply may work!
You will need to use an older iTunes version and once it is downloaded and installed on your computer, at launch, hold down the Opt/Alt key on your keyboard while launching this older iTunee version, so you can create a new Tunes library.
BEFORE DOING the IMMEDIATELY ABOVE, if you use iTunes on a computer and already have an iTunes Library, you will need to find the iTunes Library folder on your computer and, temporarily, move/copy this folder to another location so you do not accidentally write over your existing current iTunes library.
Then, back on your older iDevice, 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 iDevice.
If you are successful in getting apps on this iPad, consider looking for more “up to date”, third party iOS web browsers for that version of iOS.
Some third party web browser developers supported their web browser on iOS 9.3.5 and are more up to date than the over two year old iOS version of the Safari Web Browser.
If you use iTunes on a computer, some third party iOS web browsers that may still have older versions for iOS 9.3.5.
Perfect Web browser
Dolphin Web browser
iCab Mobile Web browser
Maven Web Browser
Opera Web browser
Maxthon Web browser
Good Luck to You!
