older ipad trying to add google chrome says not compatible. How do I make ipad compatible?

You don't.

Upgrading/updating that iPad any farther will never, ever be possible.

If your iPad model has been stuck on iOS 9 for all of these past years, then you own an 8-1/2-year old, 2012 iPad Mini 1st generation.

That iPad model cannot ever upgrade beyond iOS 9.3.5/9.3.6/

Your 8-1/2-year old, iPad model is too old, now.

Apple ended support for all 8-10-year old iOS devices well over 4 years, ago, in 2016.

Third party app developers abandoned and stopped supporting these 8-10-year old iOS devices nearly 3 years, ago, in 2018.

There are, virtually, NO MORE third party apps available from the iOS App Store, any longer!

Third party compatible apps for such old devices are few and far between, now, in 2021.

AND, that well over 4-year old default iOS Safari Web browser is too old, not secure and not safe to use to access the Internet, any longer.

There are virtually NO MORE third party Web browsers left for 8-10 year old iPads!

Available and more popular third party Web browser choices are pretty much GONE, now.

If you must use these old iPad models, here is what is left for still updated Web browsers.

Pickins’ are slim, now!

ALook Web browser ( A fairly new Web browser primarily designed for old iOS device versions, but is still available to newer iOS/iPadOS devices, as well )

Dolphin Web browser

Maxthon Web browser

TOR private browser

TOR + VPN private browser

Turbo VPN private browser

This is pretty much it for iOS 9/10 compatible, third party Web browsers today.

Simply put, a 1st gen iPad Mini is too old and obsolete now.

Sorry, but this is the reality for ALL 8-10-year old AND OLDER iOS devices now. Especially going into 2021!

There is one last thing you can try/attempt, if you need an older version of an app.

If you own much newer iOS device that can run either iOS 12 and.or iOS/iPadOS 13 and later, you can install the most recent app/s onto that more recent iOS device.

Then go back to your older iPad, open the iOS App Store, go to the Purchases section of the store app, search for the app/s you wish to try and download to that older iPad and see if an older version of the app is allowed to be downloaded/installed to that older iPad.

These newer iOS/iPadOS devices must use your same Apple ID user account and password as the older device you ard trying to get an older app for.

Failing that OR IF NO joy, then there is nothing more to be done.

It's 2021 now!

If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted Apple product/device retailers/resellers, locally or online, capable of running the latest iPadOS versions.

There are PLENTY of newer, older iPad models that can run the latest, current versions of iPadOS.

I am sorry that you had to learn all of this, but this does not change any of the facts regarding these very old iOS devices.

Sorry & Best of Luck to You!

The Chrome Browser requires iOS12.2 or later.

iPad2, iPad3 and iPad mini1 can only be updated to iOS 9.3.5 (WiFi Only models) or iOS 9.3.6 (WiFi & Cellular models).

Apple ended update support for these models in September 2016. Your iPad cannot be updated to iOS 10 or later major versions of iOS, as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS. This limitation cannot be bypassed; these are 32-bit architecture devices, whilst all recent versions of iOS/iPadOS are designed for 64-bit hardware platforms. iPad2, iPad3 and iPad mini1 are obsolete.

You may wish to consider that compatible Apps for your iPad are increasingly difficult to find - as third-party developers are dropping support for all 32-bit devices and increasingly for older 64-bit versions of iOS preceding iOS11/12/13. As older versions of Apps are removed from the Apple App Store, you’ll not be able to (re)download or install them - which may severely limit the usefulness and utility of your iPad. As such, if you want or need to access most current Apps, requiring more recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model.

Of current models, even the entry-level iPad8 has specifications and capabilities that will massively outperform you current iPad - and is compatible with the vast majority of current Apps. Other models are more powerful still.

I hope this information provides helpful and succinct clarity as to your available options - and the limitations of your current iPad.

it's googles choice which versions of ios they wish to support with their chrome app, so your options are

1. not use chrome
2. convince google to support older versions
3. purchase an ipad which support the minimum ios version the chrome app requires

Chrome requires iOS 12.2 or later.

If you can't update to ios 12.2, you can't install it.