https://letsencrypt.org/docs/acme-protocol-updates/
https://community.letsencrypt.org/t/end-of-life-plan-for-acm...
So this has been planned for quite some time, and if you have a current Letsencrypt client, it should keep working seamlessly.
But yeah, if you have servers running an old OS release that won't get a new certbot version, that's gonna suck.