For the last few candidates I interviewed, I had prepared the following process:
a ~1-hour conversation to get a feeling of the person (in person until the pandemic hit, then via MS Teams), chatting about their past experience, current work, personal interests, involvement in the community etc.
a sample project to work on, which they had to clone from GitLab (via git), get the problem statement (requirements) from the readme, and describe in words how to solve the problem
another short conversation about their reply and suggested solution
implement part of the requirements in the sample project and submit the solution via GitLab (git)
another conversation about how they solved it, why, etc.
Regarding certifications, I recently posted to LinkedIn about my opinion on them.
Edit: The project mentioned above is an actual project of ours, where we had to implement some small changes to a very badly written piece of legacy code with no encapsulation, documentation, etc.