Have you tried the demo version? If only to rule out issues with SafeDisc, since even the no-cd cracks might have remnants of that left in.

Just tried the multiplayer demo and got the same error, unfortunately.

Have you installed any unofficial Service Packs to your Win98SE installation?

No, it's plain Win98SE English. Besides the drivers and DirectX, the only extra system component I can think of is the USB drive support nusb36e and Daemon Tools 3.47.

I tried installing NUSB and Daemon Tools in a PCEm VM, where the game ran and either didn't affect it. Vortex and GeForce drivers refused to install without the hardware, so I couldn't test those. However, one possible culprit could be that the VM has Win98 with the default US codepage installed and there's a central european codepage on my retro PC. Sadly, this setting can't be changed without reinstalling the entire system.

That's a good catch and perhaps it's the culprit. I would also perhaps try uninstalling Vortex's drivers, though removing it should be enough.

After trying many different combinations of things, I finally figured out what the issue was.

When installing Win98, I didn't tick the box with "Communications" components. Renegade crashes without them. 🤦‍♂️

The components can be easily installed via Add/Remove Programs in the Control Panel.

Project Eden has a similar issue. If "Dial-Up Networking" is not installed, the game throws an error at launch, asking for "SVRAPI.DLL".

Well at least that's a proper error message, as opposed to C&C:R's page faulting with zero info regarding the cause.