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. The 32-bit platform upon which the iPad4 is based is obsolete.
Many App Developers have also dropped support for older devices and iOS versions preceding iOS11/12/13 - and have withdrawn older versions of their Apps from the Apple App Store.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 Once compatible versions Apps are withdrawn, you’ll not be able (re)download or (re)install them.
Apps integral to iOS, such as Safari, are only updated along with the Operating System. As a consequence, the embedded web browser is approaching four years of age. Many websites will require your browser to meet current security standards - which will likely be lacking on such an old version of Safari. A feature of iOS is that all browsers, such as native Safari and third-party (such as Firefox), share a common codebase (WebKit); as such attempting to use an alternative browser with iPad4 will be unlikely to resolve any issues in this regard.
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 iPad8 supports current iPadOS 14 - and has hardware specifications and capabilities that vastly outperform an old iPad4.
I hope this information is helpful - if only in clearly stating the limitations of your iPad4 and your available options.