See the related release announcement:
Plex Media Server 1.19.3.2740 is now available in the Beta update channel
FIXES:
- (Security) Remove the Windows AppData path preference from the web app (#11355)
From what I understand you can still change it manually through the settings in your registry.
https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/
LocalAppDataPath
Values: path Description: Set the location of of the Plex Media Server data directory (Windows only). Example: D:\Data\Plex\Data
