Hello. I am new to speedrunning and am curios if I could just submit a run with the in game time instead of using a program like livesplit. Thank you.

you can i sumbit speedruns with the game time all the time thou not for the demo

Why not the demo?

The Ghostrunner demo uses in-game time as the standard timing method.
So the answer is yes.
(This is also in the rules.)

As Ekorn said : for demo we use In game time.
for full game runs we prefer if you did have auto splitter unless you are on console or if there is good reason to not use it on PC.
Since re-timing runs takes a lot of time.