The error log is saying that your cache folder is not permissioned properly. Whatever user is running Grav also needs write access to the cache folder. Revisit the Permissions docs and double check that your user/group settings are correct. There’s also a specific Digitalocean page you can look at, too.
@Rhuksteronce recommendedServerpilot.io to me to setup a Digital Ocean server for Grav, which has basically allowed me to forget something called “permissions” exist.