There has never, ever been a native calculator app for iPad.
Apple never finished developing or designing an acceptable and unique calculator app for iPad.
And, for the past 10 years, now, since, there is a whole third party, iOS App Store marketplace/cottage industry for a plethora of exceptional iPad calculator apps, now!
So, a native iPadOS calculator app for iPad is, now, not even being considered, any longer, by Apple.
Apple had an opportunity to create a unique iPad calculator app for iPad with the totally redesigned iPadOS, but Apple, once again, squandered this perfect opportunity.
Tap and read the story below.
https://www.cultofmac.com/421893/why-the-ipad-has- never-shipped-with-a-calculator-app/
Also, YouTube video with an included interview with Craig Federighi, from Apple on why NO calculator app for iPad/iPadOS.
https://youtu.be/WK_AtW66XI0
Craig Federighi, from Apple, interview is at the 2 minute 50 second mark of this video.
Apple just has a lot of other priorities and a calculator app aimed/designed just for iPad is no longer one of Apple’s priorities.
Apple has waaay too many other irons in the fire, already.
You will need to go to the iOS App Store and decide on a free or paid ( to remove ads ) third party calculator apps.
If you are one of these groups of users who is, vehemently, opposed to paying any third party iPad calculator app developer for their work in creating such apps, here is, but one totally free ( no ads ) calculator app that you can add to your iPad, from the iOS App Store .
Sci:Pro Calculator.
https://apps.apple.com/us/app/sci-pro-calculator/id684978583
There are many more third party calculator apps. Some free with ads.
Others that range from $0.99- $2.99 that offer both no ads and additional features that add value to their calculator apps.
The choices are up to you.
I use Calc-Pro HD for iPad and Digits
Calc Pro HD -iPad Calculator
https://apps.apple.com/us/app/calc-pro-hd-ipad-calculator/id457004119
Digits Tape Calculator
https://apps.apple.com/us/app/digits-tape-calculator/id364500115
PLENTY of third party calculator apps, for iPad, to choose from.
Best of Luck to You!