Can’t find any Browser choice on my iPad.

Safari is installed by default. Other web-browsers - such as Firefox, Chrome, Brave etc. - can be found and installed from the Apple App Store.

When you have installed one or more additional browser Apps, you can select the default browser from iPad settings.

Andyeippert wrote:

There are several websites I attempt to go to, including my doctor’s appointment confirmations, and a window pops up telling the browser I’m using isn’t supported.

Safari is Apple’s built-in browser. There are other third-party browsers (such as Google Chrome, Firefox, Microsoft Edge etc), but most have reliance upon the same core WebKit libraries.

Some websites incorrectly identify your iOS/iPadOS Safari User Agent when used in one or other of its browsing modes - of which there are two - these being Desktop and Mobile. Misidentification of the browser Agent can often manifest as the website reporting that your browser is out of date, or won’t properly render a page.

It’s easy to switch between modes if a website isn’t functioning correctly. From the desired web-page, touch the aA icon at the left of the Address Bar; this will reveal a menu. From the menu select Website Settings, then select (or deselect) Request Desktop Website, then tap Done. Now refresh the webpage.

The chosen setting will be saved for the selected website - and can be simply reversed if needed. For websites that have most issues with browser compatibility, Safari is often the browser most likely to work - if you choose the correct mode.

As mentioned by ChrisJ4203, you can select your default browser:

Change the default web browser or email app on your iPhone, iPad, or iPod touch - Apple Support

Andyeippert wrote:

I have the Firefox, Duck Duck Go and Chrome apps. I can see browser selection on my iPhone 11, but it just doesn’t show that choice in settings anywhere on my iPad. It is running the current IOS.

Why are you looking for a choice in settings? What setting are you trying to change? Do the browsers work when you launch them from the home screen?

What version of iPad do you have and what version of iOS/iPadOS? It seems you may not have the latest version of iPadOS if you are not seeing that setting. That link I provided says you need to have iPadOS 14 or higher. Except for the browser apps that you describe, Safari updates with iPadOS, so if you have the latest iPadOS, you would have the latest version of Safari. It is possible that these specific websites may not support those browser apps.

See this, Change the default web browser or email app on your iPhone, iPad, or iPod touch - Apple Support

It may be that those websites aren't set up to handle mobile devices (though that would be pretty pathetic). Have you tried Safari?

I still have no way to select a browser in settings.

As mentioned, you do NOT select a browser in settings.

A browser is an app - just select it on your home screen or app library.