With iOS 5.1 installed, you have a first generation iPad. The iPad1, along with other 32-bit architecture devices, are fully obsolete and are no longer supported.
Compatible Apps for your iPad are no longer available - as third-party developers have dropped support for 32-bit devices and many for iOS versions 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 iPad9 has specifications and capabilities that will massively outperform you current iPad - supports both current iPadOS16 and soon to released iPadOS17 - 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 fundamental limitations of your current iPad.