I want to upgrade my macOS Catalina to macOS 11?how can I solve the problem?my MacBook model is mid2012

If the user whats the latest and greatest versions of macOS, all is not lost.

Explore the Apple Trade-In  Process where the Value of the exiting device could be used against the cost of a new Apple Computer, iPhone or iPad  

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Have used both previously and have been satisfied each time.

pari6247 wrote:

upgrade my MacBook mid 2012 to macOS 11

You can't. MacOS BigSur is not compatible with your old computer.

macOS Big Sur - Technical Specifications

Catalina 10.15.7 is the latest version your MBP can run.