4.19 LTS was last patched on 2020-09-03 at the time of this writing and the reason why Manjaro supports multiple kernels. Bumblebee is in the same situation anyway: it receives patches but no new development.
If the 4.19 kernel solves your Bumblebee issue then that’s the solution…
P.S. Most people think that the latest new kernel is what you need all of the time but this is not true: You only need a new kernel if your new hardware is not supported by an older LTS kernel.
I needed 5.7/5.8 for a key feature. Sadly, these kernels break bumblebee and triple-click as middle-click functionality in Manjaro, which are pretty important on this particular laptop and my use thereof.