How to delete the High Sierra installation file?

I am on Monterey, but recently I needed to install High Sierra on another Mac, so I needed to download the installation package. Now, I cannot delete the installation package. When I try to empty the trashcan, I get this error message:

My OS is in Danish, but the error basically says that the trashcan could not be emptied, because some files are either locked, write-protected or some access rights are not correct. In the installation package, there is only file, which I looked at in the terminal:

I tried to delete it, change the owner and access rights using the terminal (using SUDO), but nothing works. It consistently says "Operation not permitted".

Any tricks?