There isn't one. As far as the apps are concerned, you do need to update your iOS - but as the iPad is 12 years old, you cannot.
The only workaround that might work would be to use a device with a later operating system to get the apps that you want from the app store, then factory reset the iPad so that it gets the apps from there when you login with your Apple ID. If the latest version is not compatible with iOS 9.3.5 it should offer you the option to download the last compatible version. I had tried doing it with a laptop on iTunes to the iPad 3 in 2019 and it didn't work then, but I didn't have another device to try the device route that I had read would work.
The iPad will then run that provided the app developer has not dropped support for that version. Banking apps will not work for sure, as the banks eventually force the update for security reasons.