While the 5.4.x Linux kernel hasn't been marked as stable in Gentoo yet I've updated my generic kernel configuration file to match it. As with the previous config files for 4.14.x and 4.19.x this configuration is based on the Fedora kernel with some Gentoo-specific tweaks. It supports practically every bit of hardware in existence and enables a lot of bleeding-edge kernel functionality. The downside is that building it will take a while and the modules will occupy quite a bit of storage.
Note that this kernel configuration is for use with OpenRC. If you're using systemd you'll have to remove the CONFIG_GENTOO_LINUX_INIT_SCRIPT=y line from the configuration file and add CONFIG_GENTOO_LINUX_INIT_SYSTEMD=y instead.
To use it install the appropriate sys-kernel/gentoo-sources package (5.4.x), copy the configuration file under /usr/src/linux/ and rename it to .config then proceed to build and install the kernel as usual.