YES, you can develop, support open source/Free Software (FOSS) projects as an unpaid hobby, just for fun.
YES, you can develop and support #FOSS projects as (big or small) part of your paid job or as freelancer.
YES, you can develop and support FOSS projects by asking for donations.
And yes, all of these approaches can exist at the same time. YOU decide. FOSS is about freedom, not about money or not.
And NO, you owe no-one an explanation or justification on why you do #FOSS the way you do.
And, very important:
YES, you are always free to decide to stop or reduce spending your time on FOSS and focus on more important things in your life.
FOSS should be fun, satisfying, rewarding and a positive part of your life. YOU come first. Never forget!
@jwildeboer
Martin Fink's book The Business of Open Source IIRC listed I think 14 different ways (for HP) to make a living from doing Open Source. And then there is satisfaction and hobby besides.
I think too few prizes are given.