It is not a stable platform (it is also not secure).
Linux is flaky.
And that's why it's running 38.8% of the top 10,000 websites, 100% of top 500 supercomputers and it's kernel runs on vast majority of IOT appliances, android smarphones/tablets, smart TVs, gaming consoles, Tesla cars etc. Did I already proved my point that Your opinion about GNU/Linux is in fact an OPINION and to be precise, opinion not based on facts.
The problem being there are 100s of Linux distributions
And 3-4 major ones with compatible derivatives. However flatpacks/appimages etc. are a solution for this. We're not living in 2014 anymore so please revise Your view with current situation. You don't have to package Your app for 100 distros and dozen of architectures to be compatible with every distro or choose to support one to be safe.
Several of the tools I worked with have been used to analyze the Linux kernel and distros.
And I understand You had the pleasure to examine MacOS and Windows kernel too and it turned out to be well optimised and 100% safe code? No? Oh..
There are multiple cases of malware being inserted to the Kernel by ghost contributors.
Can You direct me to any place documenting this incidents? Obviously I can find info about inserting code with deliberately added vulnerabilities but a malware? And multiple times? That's thrilling and I can't wait to read more about it.
This is why Linux is banned from critical systems. (see Do178 for aviation)
Oh boy. It's not "banned". It's just not approved as it's not designed as RTOS system. Same for ANY desktop OS so it's not even an argument in this debate You started. BTW there are RTOS kernels in FOSS world and also ones approved in Do178 eg. LynxOS.
As a desktop OS Windows is a safer bet than Linux
With no public audit and their devs contantly occupied with nonsense like adding VR functionality to any Windows tool and then provisionally riping it off to mold Windows 11 which is rougly a 20GB of blob to maintain? With no fully grown app repository and users scavenging random sites for executables? With bunch of apps working only ran as admin user and users accustomed to trying it? That's not a role model for safety but a miracle that it works somehow.