Using a drawing tablet on your lap

This is something that might work for you. I have tried it but, it was not a great experience.

The tablet is unsteady in the lap

Something like this may help https://www.nytimes.com/wirecutter/reviews/best-lap-desk/

Dealing with fall damage

Because it it is unsteady in the lap, you might drop your tablet on the floor.

If you are using a pen tablet, it probably won't damage the pen tablet.

If you are using a pen display, it's even more dangerous because if it falls from your lap your pen display is very likely to be damaged.

Eye gaze

For a pen tablet your eyes will be looking at a monitor and not at your tablet. This is the same when the tablet is on a desk or in your lap.

For a pen display your eyes will be looking at pen display. Even when the pen display is on a desk, this might cause some neck or back strain. When the pen display is on your lap, you'll be looking at more of an angle and that might cause even more strain.

Hands in different locations

I found it slightly awkward to keep one hand on the tablet and another up on the desk to use the keyboard - I use a lot of keyboard shortcuts when I draw.

Switching between drawing and typing

When the tablet is on my desk this is easy.

When the tablet was on my lap it was very awkward to move between drawing and typing because my hand had to travel too far.