Run unsafe code in serverless environments

I need to run an executable, or rather, C++ code in the cloud, and my options are Cloud Run & AWS Lambda because they are serverless and I only pay for what I use.

I thought about compiling this C++ code using Emscripten to WebAssembly. I even did a PoC using isolated-vm, however, I had difficulties in obtaining the stdout (a requirement), as the emsdk does some abstractions.

Then I tried cgroups with namespaces inside Docker, but apparently, I cannot create a cgroup within Docker since it is already running inside a cgroup.

What options do I have left?