Is there a way to securely empty trash in Big Sur?

If you have anything but a spinning hard drive - SSD or flash - there is no longer a secure delete option because of the way data is written and deleted on those drives. Once something is deleted, it is gone. If you want to be sure, you can encrypt the drive and then reverse that - that will be as secure as you can get. Or you can fill up the space with nonsense (movies?), erase, and do it again and erase again.

It would be helpful if you could explain what your concern/problem is. When the Trash is emptied, the deleted data can not be recovered except with the use of very expensive software which is used by professionals. Even then recovery may not be possible is the erased sectors of the disk have been written over with new data. I wouldn't be concerned if I were you.

What's changed is that you have your disk encrypted, right?