Is it possible to resize a large picture by file size and not resolution?

Late Edit
Let me qualify this 'simple' solution by saying that such as LinkedIn, same as any other social media site, will not care a jot what size an image is, so long as it falls over and under certain sizes in [mega]bytes [& possibly over or under a certain size in pixels]. They're not photographers or graphic designers, their interest is simple repeatable presentation in a massive multi-user environment.
They will even quite likely crop &/or re-compress behind the scenes to fit their own ideals. All you need to do as a user is give them a small-enough file to start from. You don't need to tweak to any kind of exact file size.

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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.

You can use ImageMagick:

convert original.tif -define jpeg:extent=9MB output.jpg

And quoting one of the comments:

IrfanView will allow you to do it, for those on Windows who are afraid of the command line

You can do this easily with LViewPro, a photo editing application written for Windows. One version now commonly used was originally written in 1996 for Windows 95, but works perfectly in Windows 10 64bit even though the software is 32 bit. The LViewPro photo-editor is freeware, just search for it and download. To use LViewPro, start the application, simply import your file, and in the Edit dialogue select Resize. When you do this, the dialogue box will show a New size/Current size ratio frame; make sure the Preserve aspect ratio box is checked, and select the new size of your file in a dimension-scaled percentage of the original. You can see the results in the editor before saving, or undo/redo and rescale to a different size. Remember, the file size in megabytes of the resized file will be the original file size scaled by the square root of the ratio you choose. For example, dimensional rescaling an original file to 50 percent will result in a new file size that is 25 percent of the original. The reason for this is obvious, with a bit of thought; each linear dimension of the original photo is rescaled to 50 percent of the original, meaning the rescaled photo has one-fourth the area, namely one fourth of the size of the original. Save the new file under a different name, say, 'blah-blah_rescaled-by-x-percent' so that your original is preserved. You can compress your file if you wish to reduce its size further without loss of resolution.

Usually, when one creates, saves or converts an image, they choose the image format, geometric size (in pixels, width and height), color scheme and depth, compression type and settings (the amount of detail alowed to get lost) and that's it.

The file size is not usually set, it emerges from the image content and settings.

Of course, one can play with these settings and tweak them until the file size becomes acceptable. Maybe there is a software that can be made to tweak the compression settings for you for a given size.

Pretty much ANY image manipulation software can rescale and convert an image. Even a recent version of MS Paint (Windows built-in) can do the trick.

For linkedin purposes, TIFF format in particular is not good. You want to save the image in JPEG or PNG format - and if you are not in a photomodel/actor/the likes business, no one will make a difference for anything above 1/4 of megabyte photo.