Other commenters saying it isn't used as a verb are wrong. They're correct that people never say "I open-source softwared my last project."
However you can definitely use "open-source" as a verb: "I open-sourced my last project." It's pretty common. And in this case "OSS" stands for "open-source", not "open-source software".
What's confusing you is that when we use the abbreviation "OSS" we're really intended people to read that as "open-source" even though the abbreviation technically means "open-source software". btw, you would never verbally spell out "OSS"—chiefly because it's the same number of syllables as "open-source".
However you can definitely use "open-source" as a verb: "I open-sourced my last project." It's pretty common. And in this case "OSS" stands for "open-source", not "open-source software".
What's confusing you is that when we use the abbreviation "OSS" we're really intended people to read that as "open-source" even though the abbreviation technically means "open-source software". btw, you would never verbally spell out "OSS"—chiefly because it's the same number of syllables as "open-source".