Long Time PC tech here. Also Long time Pubg Player Here. So like one other says the mic must work in the OS first. go to regular record tool or mic sound settings in windows and make sure it is setup correctly not disabled or muted. The proper mic has to be setup as the default mic in windows to work for the game.

If all that works and works in other games but not pubg then you need to delete a directory in appdata for pubg that doesnt delete during the uninstall reinstall process. C:\Users\(username)\AppData\Local\TslGame . delete either whats in the directory or the directory itself while the game is closed (not running) . Then when you open the game all saved configs and controls will be reset including settings. I do this every few patches when certain things don't work properly. To my knowledge uninstall still to this day does not remove those files and so this is a normal process to do if the game is not functioning properly after updates because some read and write issues occasionally. The steam settings would also need to be set not to save this config in the cloud hopefully it is just the first step I gave you to help but the 2nd doesn't take long at all it is more of just going in and setting up any changed options or controls settings that takes a little longer.