Note:
(a) The Dw.com has an English-language report dated yesterday (Oct 24) and titled "Bulgarian Air Force Pilots Refuse to Fly Outdated MiG-29 Jets" also cited DPA and AFP, so does a RadioFreeEurope RadioLiberty report (published today in English).
(b) Mikoyan Mig-29 https://en.wikipedia.org/wiki/Mikoyan_MiG-29
(table: Introduction 1982, Status In service, Produced 1981–present, Number built 1,600+; section 5 Operators: China not among them)