IPAD 14.3 update can’t be installed

To reiterate, iPadOS 14.3 is current. At this time, there are no other “point” updates to the production version of iPadOS.

However, if you have joined one of Apple’s beta programmes, you may be be seeing availability of an update to the currently installed beta version of iPadOS. That said, if this applies to you, nobody here can offer any assistance; the Terms of Use that govern participation within these Support Communities disallows any discussion of beta software.

If you are currently enrolled in a beta programme and wish to return to using the current production version, this support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

iPadOS 14.3 is current. If this version is installed, as indicated in your post, then you already have the most up-to-date version of production software.