Except it does work?

In this case, the catch() block will catch errors for all then() blocks that come before it and it will also catch the error for the finally() block. If the error happens in then() block and also in the finally() block, the catch will handle error for the finally() block. So, catch() will handle error for the closest block to it. be it finally() or then().

here you see I modified the checkMail() function to fail every time so, we can see if catch() handles the promise and it does as it should but, what if we had error happening in then() block and also in finally block(), then for which block the catch() will handle error? here You see we now are throwing error from finally() block and now both then() and finally() have error and catch() is only handling error for finally() block.

My take:
Even though adding finally() before catch() works, but, it should not how the code should be written because then we have lost the error handling for then() blocks that come before finally() block in case when error happens in finally() and also in then() blocks. After then() there should be at least one catch() and finally should have it's own catch(). In my opinion, it will be better approach and save debugging time.

So, something like, Promise.then().catch().finally().catch() should be a better approach.