To fix the clock for 1.21.4 (not sure if it works in older versions from schematic):
1) remove the two observers nearest the clock that trigger the flying machine (they face the observers facing upward with dust on them)
2) remove the two pieces of redstone dust pointing into the dropper containing the 11 counter items
3) remove the two blocks where those two dust were placed and move them two blocks up
4) place a target block next to the dropper with the 11 items and a redstone dust next to that, connecting back up to the dust on the observer
5) replace the two observers that trigger the flying machine
This should allow the clock to countdown properly.
1) remove the two observers nearest the clock that trigger the flying machine (they face the observers facing upward with dust on them)
2) remove the two pieces of redstone dust pointing into the dropper containing the 11 counter items
3) remove the two blocks where those two dust were placed and move them two blocks up
4) place a target block next to the dropper with the 11 items and a redstone dust next to that, connecting back up to the dust on the observer
5) replace the two observers that trigger the flying machine
This should allow the clock to countdown properly.