Nah. You can't throw a crossbow unless you have a bolt to drop on the ground. As per the "Ammunition" property.LOL so how about this:
My 8th level fighter with STR 20 (or whatever, as long as it is better than DEX) picks up a light x-bow and throws it at an orc 50 feet away under 3/4-cover.
He has Archery Fighting Style, granting him a +2 on the attack roll. After all, the light x-bow is a "ranged weapon".
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He has Tavern Brawler, so has proficiency with Improvised weapons so still gets to add his prof bonus on the attack roll.
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He has Sharpshooter, so can throw it up to 60 without disadvantage and ignoring the cover in this case.
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Since this is an attack with a ranged weapon with which he is proficient, he accepts the -5 to hit for +10 to damage.
All-in-all, he is +5 to hit (+3 prof, +2 archery) and will do 1d4+15 if he hits, killing the orc.
Should this happen? No, probably not. Once the light x-bow is thrown it becomes an "improvised weapon", but by the rules it IS a "ranged weapon". It is also a "ranged attack" because he throws it.
Add the SA to this as well:
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So, yeah, a "ranged weapon attack" means a ranged attack (he throws it) with a weapon (which, it is, even if improvised).
Have fun with that one.