Imagine, if I monitor some java and/or apache process in Solaris with the help of manual injection. I suppose I can turn it into cloud-infra mode afterwards in dynatrace dashboard? Yes or no?
And if the answer to the previous question is yes, then I wonder can I directly switch it to cloud-infra mode without doing any manual? (i.e like the way we do to any other non-Solaris OS)
No, you cannot switch to the infrastructure mode for Solaris agents. I think you can't do it also for any other PaaS type agents. Fortunately, agents for other supported OS have the full version as well.
If you still need to monitor just some infrastructure metrics without instrumenting any processes on Solaris, I'd suggest doing it remotely via ActiveGate plugin.
Another alternative is to inject OneAgent into a dummy Java process on that host but otherwise doesn't do anything. 3 lines of Java will suffice. This provides a full OneAgent context on the host to collect Infra metrics without worrying about specific apps having to be injected.