The RPi Foundation has been actively developing the 5.10.y kernel for some time with plans to switch to it as the default kernel once deemed stable. Eventually, the official linux-raspberrypi4/linux-raspberrypi kernels will move from the 5.4.y branch to the 5.10.y branch.
For now, I am building and testing a linux-raspberrypi4 package for aarch64 and am making it available to the community. If you would like to use/test it, you have several options:
1. Use my unofficial repo, instructions are here. Note that I am only building for aarch64*.
or
2. See my fork of PKGBUILDs and build your own kernel.
*I am also hosting a kodi-rpi-git package for aarch64. It has the same hardware accelerated decoding as the official package for armv7h.