macOS Catalina File Structure: Cannot remove
Apple documented that the system will be read only publicly during wwdc. 




https://devstreaming-cdn.apple.com/videos/wwdc/2019/710aunvynji5emrl/710/710_whats_new_in_apple_file_systems.pdf


You can read more in the public videos and apple developer / beta / seeding discussion forums and possibly in whatever release notes came with how you obtained your beta build of macOS. 

I don’t have a system to test, but use the same ls command as on Mojave and earlier to check flags and you might find these are protected via SIP and you would need to disable SIP to make temporary changes as an admin. The video says you can disable SIP and make changes, but the protection is engaged again after every restart and updates should be expected to replace and repair any altered files.