It is not possible to run commands at the end of a tick. The "load" and "tick" function tags allow only to run commands at the start of a tick. This really limits the possibilities of commands since you might want to wait for the game to process certain events in a tick before running a function in the same tick. It has caused some serious issues with my data pack projects. Please add a new tag to run commands at the end of a tick. Between Block entities are processed and game saving might be the best option. Thank you in advance.