Welcome to the forum ingsok.
It is most often a option to not have time/date & speed stamped on the footage of a dashcam if you dont like that.
Mind you if it is from a fear of incriminating yourself, then the speed can always be determined from the plain video itself, as a result of distance ( between 2 things in the video you can go measure ) and the time it took in the video for you to cover that distance.
This could be XX Meters between lamppost "A" and driveway "B" in X.X seconds, then it is just simple math to scale up to km/h speed.
No court of law would take the speed of a generic uncalibrated / cheap GPS antenna as evidence, but video - distance - and time are things that are hard to dispute, and those together will also give you a 100% accurate speed.
Personally i do not mind the time/date and speed at the bottom of the video, that is always the dashboard anyway so it is not in the way of anything important.
Some models with a tethered GPS antenna, you also have the simple option of just not connecting the antenna, then you just have to enter the time/date in the camera yourself, or i suppose use the default time /date.
The cameras save the video segments named with the time/date of creation + a number, so it need something to name by and deduct what files are the oldest ones and then up for deletion once the memory card are full, in order to make room for new recordings.