Can't download nothing on this iPad 4th generation it's says I need os 11 at least what can I do here

https://en.wikipedia.org/wiki/IPad_(4th_generation)

iOS 10.3.3 is the latest version supported for that model

if the app developer choose not to support older ios versions than 11 there your 3 options are

1. purchase a new ios device that support ios11
2. convince the app developer to begin supporting older ios versions
3. not use the app and maybe find an alternative one which support older versions of ios

If your iPad is currently running, or cannot be updated beyond iOS 10.3.3/4, then have an iPad4.

Update support for iPad4 ended September 2017. The final iOS releases for this model were iOS 10.3.3 (WiFi Only models) and iOS 10.3.4 (WiFi & Cellular). iPad4 cannot be updated to any later major version of iOS as it lacks the minimum hardware requirements needed to run more recent versions.

Many App Developers have also dropped support for older devices and iOS versions preceding iOS11/12/3 - and have withdrawn older versions of their Apps from the Apple App Store. Withdrawal of Apps supporting older models of iPad is making their utility and usefulness significantly more limited. Once compatible versions Apps are withdrawn, you’ll not be able (re)download or (re)install them.

If Apps that you need to use now have higher minimum iOS-version requirements, your only option is to replace your iPad with newer model. Of current models, even the entry level iPad7 supports current iPadOS13 and soon to be released iPadOS14 - and has hardware specifications and capabilities that will vastly outperform your old iPad4. Other models of iPad offer a step-up in performance, features and cost.

I hope this information is helpful - if only in clarifying the limitations of your iPad4 and outlining your available options.