GitKraken won't push to new remote ("Select remote branch to push/pull with 'master': ")

You'd need to "Set Upstream" for your local branch. To do so:

• Find your local branch on left pane under LOCAL,
• right-click and select "Set Upstream",
• name your new remote branch on the prompt and click "Submit",
• click "Push" on the top toolbar.

To avoid confusion, you could also name your local branch (to keep it the same as the remote) at the time of creating the branch from master or whichever remote you want to branch from.

Note: Though there shouldn't be drastic differences between versions, the above is based on GitKraken 2.5.0 64-bit (non-pro version)