Installing a firmware version meant for the 1GB RAM model on a 512MB board will often cause a permanent boot loop.
You cannot update the MSD338 via USB flash drive like a smart TV. It requires a USB-to-TTL serial programmer (also called a CH340G or PL2303). cvte msd338 512m update 2021
If you are looking at the 2021 update for this board, it is best viewed as a rather than a feature upgrade. It is intended to keep basic functions running but cannot overcome the physical limitation of 512MB RAM. For a modern experience, many users prefer bypassing the board's internal "smart" features entirely and using an external HDMI streaming stick (like a Fire Stick or Chromecast). Installing a firmware version meant for the 1GB