Try this.
Open a white (255,255,255) document covering your screen.
Soft proof using their profile (with simulate paper white set to ON).
Take a blank sheet of the paper in question next to your screen (under your 5000K viewing light) and calibrate by eye the white point of the screen to come as close as possible to the paper, then profile the display.
(All this assuming you are editing your images under softproofing with their profile).
Forgive my ignorance here, but if I might ask a basic question.......
1. How might I open a white document in Lightroom Classic & be assured that it is 255, 255, 255? As an alternative, might I not use any blank, white piece of paper to achieve the same objective?
2. In order to "calibrate by eye the white point of the screen to come as close as possible to the paper", does this suggest adjusting the brightness of the screen itself?
3. Once I achieve a reasonable match between the screen & the paper, how will I know what the new white point is so that I can profile the display to that target?
Again, forgive me if my questions indicate my lack of knowledge regarding color management. Thank you for your help.