You can also customize the Dockerfile itself, that can be found here: Docker
You would need to copy all of those lines over, and then change line 12 to PHP 7.4.33.
Line 13 should be changed to 7.4.33.
The hash on line 14 would need to be 924846abf93bc613815c55dd3f5809377813ac62a9ec4eb3778675b82a27b927.
Make sure this is in an empty folder, and run the command “docker build”, which should create the image you can then use to create a container with that uses PHP 7.4 instead.