The Pick New sprite option becomes unavailable if you change the view options to either tile or column when working with the keyframes of a 2D animation. This issue affects the project indefinitely until a new project is made, changing the project settings or editor preferences back to default does not resolve this issue. This issue does not appear to be a regression.
Versions Tested: Issue occurs in all versions tested
4.17.2 - CL: 3658906
4.18.2 - CL: 3794801
4.19.0 - CL: 3813964
Head over to the existing Questions & Answers thread and let us know what's up.