Do you have Team you're overseeing or working with?
I'd take the time to ask each member of the team, what they are working on, what problems they are having, and how you can assist them in some way.
The product your company/team is building will have a roadmap of features to be delivered, spend time with members of the Dev team talking through each of those features, what is required, how they plan to build them.
As a senior, you may not know the platform, but you can get to know how the team works, offer suggestions and identify probable pain points. There might be entire sections of code you can work out that needs to be written which don't necessarily require knowledge of the platform.
All this will take time, be incredibly useful for everyone and in your spare time you can learn about the platform.
I'd take the time to ask each member of the team, what they are working on, what problems they are having, and how you can assist them in some way.
The product your company/team is building will have a roadmap of features to be delivered, spend time with members of the Dev team talking through each of those features, what is required, how they plan to build them.
As a senior, you may not know the platform, but you can get to know how the team works, offer suggestions and identify probable pain points. There might be entire sections of code you can work out that needs to be written which don't necessarily require knowledge of the platform.
All this will take time, be incredibly useful for everyone and in your spare time you can learn about the platform.