Save (export) it from any graphics/photo app as a JPG or PNG.
I tested a 180 MB 16-bit TIF file. (Saved as an 8-bit TIF this would be only ~23 MB, which is what I imagine your photographer will be supplying.)
It saved to a 6.5 MB JPG, even at 100% quality (same size, no other adjustments). Reducing that to just a ‘high’ quality got it down to 1.3 MB. This would be more than sufficient quality for such as LinkedIn.
As an 8-bit PNG (which is a lossless format), it was 8 MB.