Firmware updates do not damage hardware displays. If you see lines or flickering after an update, it is a coincidence or a loose ribbon cable. Contact Xiaomi India service center (1800 103 6286).
Download the official firmware .zip file from Xiaomi Global Support or an authorized forum. Firmware Update on XIAOMI Mi TV 4X 50 -India-
The Mi TV 4X 50 is a 2018/2019 workhorse. Firmware updates won't give you a faster processor, but they will keep your DRM certificates (Widevine L1) valid for HD streaming. Firmware updates do not damage hardware displays