Last Jewish bakery that has been around for decades, maybe, but not the last.
Buns doesn't have a physical location (yet), but makes Jewish-style baked goods and, unlike Rainbow, even has kosher certification. Also, they aren't "Jewish bakeries" per se, but a handful of vegan bakeries (Wildflour on East Avenue in Pawtucket, Blush on Atwells Avenue) also have kosher certification. Bubbie's on Hope Street will further fill the niche when it officially opens in a few weeks.