What is oldest IPad I should buy?

I am buying an IPad for my 90 year old Mother to help her keep in touch with her adult children who live long distance away.

We only need basic functions like the ability to use apps such as Netflix, Facebook, Google chrome and so on.

I bought an older one which was an IPad Air ( not IPad Air 2 or 3) from a supposed reputable website in Australia. But when I got it, I tried to download a Netflix app, and a message said I need IOS 14.0 or higher. which the IPad Air doesn’t have access to because it’s too old.

I complained to the website saying they shouldn’t be selling IPads that don’t function as iPads anymore.

pits only function now is as a digital photo frame. They said I should have checked, it’s my own fault.

So my question is.

To access the minimum of IOS 14.0 and higher what is the oldest model of IPad, iPad Air or iPad Pro should I get that will give me at least a few years of use?

The website have credited me my purchase money less $50 handling so I have to get another one from them, so I don’t want to fail this time.

Your help is much appreciated.