My ipad 12.9 pro 2021 won't bring up the keyboard to enter my password?

There is an icon to trigger the virtual keyboard. With a physical keyboard shown, it’ll show either in the lower right corner of the display, or will show across the bottom of the display. The larger of the two is shown below. There’ll be a two-character language code in a bubble. Tap that.

If there is a hardware keyboard and it’s somehow not working, try removing it.

I’ve also met a few cases where the virtual keyboard won’t activate and the screen locked/frozen/unresponsive, and one potential fix is to use the buttons to force a restart ➡️ If your iPad won't turn on or is frozen - Apple Support

Is it paired to an external keyboard? If so use that physical keyboard to type in your password.

Otherwise, there may be an icon on screen to let you bring up the onscreen keyboard.