I’m not sure that IIs is the relevant point here is it?

I build using Microsoft technologies, and haven’t touched IIs for more than 8 years. I almost entirely use OSS projects, on linux.

From writing, to testing, to IaC, to the runtime, the server OS, the webserver, the proxy…etc is all FOSS projects these days.

The only proprietary things I used is the hosting provider itself and their services, and my IDE.