When i start the pgadmin ,pgadmin server is started along with a key value ,security token
http://127.0.0.1:5050/?key=571b59d5-aac1-43aa-88e2-38b6fa2857f4
how to disable this key generation or keep unique key
That key is needed when you run pgAdmin4 in Desktop mode to make it secure against unauthorized access from other user users on the same shared machine, In case if you left the pgAdmin4 running on the shared system where some malicious user can scan the open ports and try to access it via that port, so the security token prevents them to access your opened sessions, If you want to disable the token mechanism then you have to switch to Server mode.
For more details refer: https://www.pgadmin.org/docs/pgadmin4/dev/server_deployment.html#configuration