There are also some charities that ship old PCs to Africa, install a small Linux distro on them, e.g.:
https://www.computers4charity.org/computers-for-africa
https://worldcomputerexchange.org/
When I lived in London I helped clients donate a lot of kit to ComputerAid International:
https://www.computeraid.org/
And what's now Computers4Charity:
https://www.computers4charity.org/
There are also some charities that ship old PCs to Africa, install a small Linux distro on them, e.g.:
https://www.computers4charity.org/computers-for-africa
https://worldcomputerexchange.org/