I don't think "more than once" can get you a job, my goal was to contribute a LOT, like full-time for 3-6 months on issues that no one wants to work on so I actually impress.
That is a lot of time to work for free. Why not get a regular job and convince your employer to let you contribute to Open Source project they use.
"regular jobs" where I live, offer very bad compensation packages. I see a lot of remote companies offering good pay along with a good environment and good benefits.
have you applied and were rejected?
Yes.
just study more algorithms
You mean, if the reason for rejection was failing algorithm questions in the interview, which might not be the case.
Kernel development is actually one of the areas of programming where you do have to implement algorithms.