Agreed, that most people find certificate handling complicated…
The same is also valid for IT itself… 
Personally, I find that OPNsense does a good job of managing it’s certificates and what it presents where…
No need for an “App” to do this simple job!
My 2 cents
Andy
I am looking for a universal way/tool/mehod to deal with certs in windows and linux environments…
What do you mean by “deal with”? And what kind of certs? Are you wanting to run a local certificate authority? If so, that looks like one tool that would do the job. Step-CA is another. But do you need a local CA at all?
Forgive me my ignorance, I am not sure atm if I need it really…
Found another interesting Software for certificate lifecycle management - Dogtag
This one can maybe run under Nethserver?