I have a 64-bit Gentoo Linux running on a Raspberry Pi 2 W.

GenPi64 /home/demouser # uname -a
Linux GenPi64 5.10.92-v8 #1 SMP PREEMPT Thu Mar 10 09:38:22 UTC 2022 aarch64 GNU/Linux
GenPi64 /home/demouser #

This was made possible by the kind folks at the GenPi64 project.

To get to this point, I downloaded the following image

Raspberry Pi 4B, 3B/B+ 64-bit Lite alpha9 genpi64-arm64-openrc-lite-alpha9.img.zst

and loaded same on a Raspberry Pi 4 (8GB) and then performed an emerge update which took about 10 hours. The project is in need for manpower to help get their Jenkins packager up to snuff and when Jenkins is working (by automatically building images on scheduled events such as updates, or daily), then there will not be the out-of-sync package issue which caused me to have to upgrade for 10 hours. Once I had the high watermark of the Gentoo packages installed, I powered down the Raspberry Pi 4 and I removed the SD HC (Sand Disk 64 GB) and popped the disk into a Pi Zero 2 W and was welcomed with the traditional Gentoo status lines and a log-in prompt.

Hurrah for the GenPi64 project project!

Retired software developer 24 years at world's largest database company. Gentoo Linux, Perl, & single-board computers ("SBC") including Raspberry Pi.