Only God can be in more than one place at a time, such as being in heaven on his throne ruling and on earth visibly being seen. This is called omnipresence, meaning all, that God is everywhere present. What this does not mean is God is in everything (as taught in pantheism).

Ps 139:7-9 “Where can I go from Your Spirit? Or where can I flee from Your presence? If I ascend into heaven, You are there; if I make my bed in hell, behold, You are there. If I take the wings of the morning, and dwell in the uttermost parts of the sea” Only God is not restricted by space or location. Only God has the ability and nature to be present everywhere, this means that the totality of his person is there and is not divided..

There are those who believe that Saints from the Old Testament have visited them but heaven is a fixed place that cannot cross to earth. What about the transfiguration of Jesus where both Moses and Elijah appeared? True. but Moses was not in Abraham’s paradise at the same time he was with Elijah on earth.  He was removed from Paradise as Elijah who was in heaven was removed , to appear briefly with Jesus on earth. It is because God summoned them. It was a special unique, one time event.

Demons often pose as people that have gone the way of death, to convince loved ones that they have nothing to be concerned about. The story the story of Lazarus when the rich man asked Jesus to warn his brothers of the place he is in - Jesus’ answer was that even if one rose from the dead they would not listen (referring to one he would raise or even himself) He did not say one can visit them while they are dead, but they had to be raised.

A physical or spirit creature is obviously unable to be more than one place at a time. No creature can be 2 places at one time. God alone is omni-present. This is the great difference between a creature and its maker. The God who spread the universe out with his hand is able to see and hear all that is taking place.

For example God - the Holy Spirit can be in every believer at the same time as well as outside them.

Mt 28: 20 Jesus promised He would be with us always throughout time, in every generation..

Matt 18:20 "For where two or three are gathered together in My name, I am there in the midst of them."

Omni presence is exclusive to God’s nature only. (Deut.4:7; 1 Kings 8:27;  Acts 17:24; Heb.4:13).

Jer 23:23-24 Am I a God near at hand," says the LORD, "And not a God afar off?
Can anyone hide himself in secret places, so I shall not see him?" says the LORD; "Do I not fill heaven and earth?" says the LORD.