If you got the “download launcher ini fail 0x500000003" error when you open the PUBG Lite launcher, you should take a look at my solution.
First of all, I suggest you reset your modem and try to open the game.
If didn’t fix the problem, try to change the DNS and try to open the game. How to Change the DNS?
If DNS is already active, cancel it and try without DNS, if the error is the same, use a different DNS.
If the above solutions didn't fix the problem, uninstall the game and reinstall the PUBG Lite to a different location this time.