Sleeping separation anxiety

Our 7 year old kid has sleeping anxiety, we have tried almost everything. We limit screen time, he exercises every day, he has dinner at 7pm, takes a bath and then dad goes into bed and waits until he is asleep to leave his room. The kid is on guard trying his best to wake up and check that dad did not leave the room, so sometimes 20min after falling asleep he wakes up again and calls for dad to go to bed with him again. He wakes up sometimes up to 8 times a night. When trying to have him stay by himself without returning to his bedroom the crying, yelling, hitting doors, does not stop, and he is unable to soothe himself. We are now trying the method to have him 5 min by himself in his room and when the 5 min are done dad goes and stays with him until he is asleep. It has calmed his terror of staying alone for the 5 min that he is there, but he is still in watch mode and when he wakes up its the same crying and tantrums that we have faced. Now instead of having his dad go back to his room, we are alowing him to go to ours, at least so we can also have a good sleep, and avoid us the parents to sleep separately, but I am not sure if that is worst. Have you tried this method, are there any recommendations that you could give us?