> Do you not use non-OS package managers?

Mostly no, sometimes I give up and still use pip as a separate user.

> If not, do you develop software with source dependencies (go, java, node, rust, python)? If so, how do you handle acquiring those dependencies—by hand or using a tool

I haven't felt the need to use Go, the only Java software I use is in the OS repo. I don't want to use JS software for other reasons. This is one of the reasons why I don't like Rust rewrites. Python dependencies are very often in the OS repo. If there is anything else, I compile it from source and I curse when software doesn't use or adheres to the standard of the GNU build system.

I hope you understand you are part of a very, very small minority.