How do I make a time stop?

I want to create an assembly that will be based on control and time travel, but not one mod does not add the way I need to stop time, so I decided to create my own mod, but I don't really know how to do it. I think that for the effect of a gray screen, you can make a completely translucent gray interface, to stop entities, set a motion vector for all entities every tick ~ ~ ~ but then how to allow the player and the temporary ghost (this will be such an immortal mob that will act as an incentive to return normal time back, it will appear 20 blocks behind the player and if he catches the player, he will take away the opportunity to stop time) to move, because if I put each mob separately, then the mod mobs will be able to move. I also don't understand how to stop falling blocks, as well as the fluidity of liquids, dynamite explosion, particles and the time of day itself (in the sense of how to stop it, I know (infinitely move it to the same point in time), but how to stop it at exactly the moment that is happening now). Version 1.16.5, so it won't work to just put the command in writing, it hasn't been delivered to this version yet.
P. s. translated from Russian via Yandex translator, there may be errors.