It’s not. Tosafos says the gezeirah doesn’t apply when we don’t know how to fix instruments.
The Rama (339 syif 3) has two opinions. The first (stam) says that we don’t protest those dancing because of Mutav Sheyihiyu Shogegim (meaning it’s Asur). The Second (Yesh Omrim) says that “it’s all Mutar” because of Tosfos’ reason (we’re not Baki in making kli shir), and “it could be the reason people are lenient”. So according to Kalei Hapsak, the Halacha would be that dancing and singing is forbidden even for Ashkenazim.
But if you look in the Eishel Avraham of Butchach (to 339:3), he doesn’t say that we dance and clap for Tosfos’ reason. He says that we dance and sing on Shabbos because of Simchas Shabbos, and it’s Mashma from him that we’d be allowed to dance and clap even in the Gemara’s time (when we were Baki in making a Kli Shir). I’m almost positive the Minchas Elazar says the same thing.