Most modern TV/computer screens don't have so saturated RGB primary colors to name any particular triple wavelengths as the wavelengths of a particular monitor. Moreover, if we try to ascribe some wavelength to a primary color by applying the concept of dominant wavelength, we'll still have too much variation in actual RGB primaries in different screen technologies.
The most common color space to which the computer monitors (and, to a lesser extent, TV screens) adhere is sRGB. There we have dominant wavelengths of about 549 nm for green, 612 nm for red and 464 nm for blue with respect to the sRGB white point.
On the other hand, there are many displays like OLED TVs and smartphone AMOLED screens, which use another (more saturated) set of primary colors, e.g. Display P3. In this color space the dominant wavelengths are close to those of sRGB, but somewhat different.
And even among the displays which nominally correspond to the same color space standard, there's quite a noticeable variation of primary colors and the proportions in which they are mixed for any given RGB value. So if you have two monitors (especially of different makes or models) and try to display the same color on them, you'll notice that the colors don't match.
Color calibration is a procedure with which we can try to minimize differences of the colors displayed by a monitor from the reference color space, but if monitor's primaries are too far from the nominal, this won't lead to too good results, so some residual mismatching will still remain.