Q: Is the total number of jivatmas (both in the spiritual world and material world) fixed or is Krishna creating new jivatmas all the time?
See BG 2.20
“For the soul there is neither birth nor death at any time. He has not come into being, does not come into being, and will not come into being. He is unborn, eternal, ever-existing and primeval.”
COMMENTARY BY BALADEVA VIDYABHUSAN:
This verse confirms the eternal nature of the atma. With the words na jayate mriyate (the atma is not born nor does it die at any time), creation and destruction are both excluded.
COMMENTARY BY VISVANATH CAKRAVARTI THAKUR:
The eternal nature of the jiva is here clearly proven. The first line negates the possibility of birth and death for the jiva at the present time. The second line negates birth and death in the past and the future. Therefore it is unborn (aja): in past, present and future. Because of no birth, it has no previous non-existence (prag-abhava). It exists at all times (sasvatah), meaning that at no time in past, present or future, will it be destroyed (dhvamsa). Therefore it is eternal (nityam).
“…the soul is indestructible, eternal, unborn and immutable”