I primarily use Krita for animation, and one of the things I’ve liked since I started animating in it was how clean the timeline was. I can keep it small at the bottom of my screen and only see the layers relevant to what I’m doing.
With the change of the default state of “Show In Timeline” to true, it’s now the first thing I do when I open a file to turn this off on the default layer. And then each time I make a new layer, I have to turn this off again. And when I make a group layer, that also shows in the timeline, though I’m not sure that one even should.
I appreciate that for many people, having that on as a default may be useful, but I’ve found it just becomes something to remember to do constantly.
I would really want to have it as a setting in configuration, turned on by default (because otherwise beginners get lost 
), but possible to turn off by me and others.
I thought it was a bug and was looking here for a workaround. I hope it gets a toggle in settings as soon as possible. I miss the clean timeline too. 
I agree with you. The timeline was better and cleaner the old way. I speak for myself, but many times I have additional layers for timing/charts/… (that I just use for reference) and having them appear by default in the timeline is very confusing.
And we had more visible canvas to work with.
Please make it an option. And thanks for listening.
https://bugs.kde.org/show_bug.cgi?id=413805 and
https://bugs.kde.org/show_bug.cgi?id=414690
This will be considered carefully, I’m sure.