FLOSS opinion that shouldn't be controversial but is
If the developers of an application get mad at you for forking, they are only developing "open source" software.
Developers of "free software" thank you for forking their code, because you are taking control of your personal computing instead of just being a passive consumer.
It doesn't matter if the code you are using is licensed under the GPL. If users can only exercise one of the four freedoms in practise, it's just a PR exercise.
free software is meaningful only when it's a political demand, not a lifestyle/technical choice
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko