You're right. I couldn't access the single player by using the launcher provided by CnC, so I downloaded this one: https://www.moddb.com/games/cc-generals/downloads/new-fixed-ultimate-collection-launchers-v101a According to the dev, the warnings are false alarms.
I have tried to install the CNC client so I can play C&C RA2. However, a trojan warning came up after the installation for RA2Launcher.exe. Is this a false positive? https://www.virustotal.com/gui/file/ac7b910d392033e37b10669257e502c84400fde45b5b80bd79c38659b48a8192/detection