Drawing tablets that have an embedded display panel and those display panels have maximum typical brightness. You have been exposed to many display panels in televisions in phones and watches. Here I'd like to set your expectations about what you're going to experience in terms of brightness for drawing tablets.
Brightness is measured in cd/m2 (Candela per square meter) but that is hard to type so man people use the equivalent unit of nit.
The environment you are using the tablet in greatly affects the brightness you need. Below is my take on what you need under different conditions
indoors + dark
Low amounts of ambient light. Light conditions are not changing.
200 to 250 nits is enough
indoors + bright
Lots of ambient light. Maybe be to bright indoor lights. Maybe due to windows. If window, then brightness may change dramatically because of cloud cover.
250 to 350 nits is enough
outdoors + under shade
Overall bright environment with lots of ambient light. No direct sunlight hitting your tablet.
>=500 nits is needed
outdoors + no shade
Very bright. Sunlight hitting your tablet.
>= 1000 nits is needed
Overall, display panels for drawing tablets fall in the range of 200 to 400 nits.
Many are within the range 220 to 250 nits.
Only a few are >= 300 nits.
Here is the distribution of brightness values for pen displays released on 2020 or later.
400
2
350
1
330
1
320
1
300
2
275
1
250
9
220
16
210
1
200
3
Includes only those pen displays that have been released since 2020
WACOM Cintiq Pro 17 (DTH-172)
400
WACOM Cintiq Pro 27 (DTH-271)
400
WACOM Movink 13 (DTH-135)
350
XENCELABS Pen Display 24 (LPH2412U-A)
330
WACOM Wacom One 13 touch GEN2 (DTH-134)
320
WACOM Cintiq Pro 16 (2021) (DTH-167)
300
HUION Kamvas Pro 27 (GT-2701)
300
WACOM Wacom One 12 GEN2 (DTC-121)
275
XPPEN Artist 22 GEN2 (CD220F)
250
XPPEN Artist 24 FHD (CD240F)
250
A few tablets (only Wacom as far as I know) have fans. And these fans help to keep their brighter displays cool. The fan noise can be disturbing for some people. For others it doesn't matter.