after upgrade my os to 21.04, I don’t see the plank. please is it normal ?
No. That’s not normal.
Do check to see if you have both plank and the ubuntu budgie meta package installed.
I.e.
sudo apt install ubuntu-budgie-desktop budgie-desktop-environment plank
I suspect you may have accidently removed one of the meta packages and the upgrade assumed you didn’t need packages such as plank anymore.