Both the TCL 40 Nxtpaper 4G & 5G models use PWM (confirmed by TCL's support team).
I ordered and used the 40 Nxtpaper 4G, and returned it the following day, as I did not find it comfortable. At lower brightness levels (under 50%), eye strain symptoms developed.
At higher brightness levels, it's usable, but the backlight is harsh, and reading text on screen wasn't a great experience.
Also, when using the Nxtpaper modes, the backlight has a strong blue hue, and the eye comfort mode cannot be activated simultaneously.
Apart from the display issues, the performance of the G88 was awful. Quite laggy, slow, constant stutters and jitters.
The same nxtpaper like effect can be achieved on any other android phone, by investing in a high quality matte anti glare screen protector, and using android's monochrome/grayscale mode. If owning a xiaomi, miui's paper mode would also achieve the same effect (alongside an anti glare matte protector)