Does garçon mean (male) waiters only, not waitresses? I can’t find a site which addresses that question, though etymologically, and in French, it means “boy”.
Garçon is used only for male waiters:
- A waiter in a French restaurant or hotel.
- French, literally ‘boy’.
(Oxford Dictionary Online)
- From c. 1400 as "young male servant, squire, page." Meaning "a waiter" (especially one in a French restaurant) is a reborrowing from 1788.
Unfortunately, it is quite hard to find a dictionary entry that explicitly says the waiter must be male. The OED comes quite close, even though the wording technically separates "boy" and "waiter":
a. A boy, serving-man, waiter; in English use chiefly a waiter in a French hotel or restaurant.
You're right to point out that etymology doesn't cut it, not strictly. After all, garçon in this sense was "reborrowed" as early as 1788, very shortly after the seeming neutral sense "server" (as opposed to "male child") began to appear in French (TLFi entry 1c).
That said, it's worth noting that all nouns have a gender in French and garçon in French could only be used of males at every stage of its development. The fact that the English borrowing is used in French settings according several dictionaries' entries supports the idea that it would behave in conformity.
I'll also add my experience to that of everyone else who feels that garçon is reserved for male waiters. I think this feeling is also influenced by the widespread knowledge among English speakers of the modern French meaning "boy"; I expect that someone hearing "garçon" for the first time will usually receive that translation.
By the way, the cedilla is not optional, even though it's a pain to type. On Macs, the shortcut is Alt/Option + C. On PC, hold ALT and type 1 3 5 on the numpad.
One reason it's not optional is that it changes the sound. English speakers would generally be temped to read garcon "gar-kon" instead of the correct "gar-son" if they happened across it.
As the other commenters note, the most up-to-date answer would be that it's used of neither male nor female waiters, being seen as something of a snobism or, at best, outdated. @WhatRoughBeast's links are helpful.
As we can see from this Ngram, "garçon" is by far the least used (and a search for garçon individually shows a peak at the turn of the 20th century, followed by a tortuous but definite decline). Several times as common are waiter and waitress, and the gender-neutral server has seen a massive spike in the last two decades.