My favourite password manager is Bitwarden, and I see they have now released a secrets manager. This is an issue I have had for a while, and I like the idea of having a formal solution for distributing and controlling who can use API secrets and for updating them in apps that use them (such as Python scripts). Their 2-user 3-project plan is free.
https://bitwarden.com/products/secrets-manager/
About halfway down the page is a video that shows it in action.
I have nothing to do with Bitwarden apart from being a user. I thought this might be of interest to others.