Had an issue like this today and came across this. Just to put in my 2 cents and make sure no-one is misled by the idea of setting 777 permissions as a solution.
Setting a file as 777 is never a good idea, it makes that file or directory writeable by ANYONE and ANY process.
If your server is ever compromised, which I hope never happens, then there will be one less barrier between the attacker and your files and folders. In fact, your server need not be compromised, someone just needs to figure out a way to pass the “right” instruction to your server so that the server itself does something bad like delete all your data.
As @tkimnguyen has suggested, your setup is configured to run as a different user (plone_daemon). The solution is to launch everything as the plone_daemon
sudo -u plone_daemon bin/plonectl start
See the plone docs on this here: https://docs.plone.org/manage/deploying/processes.html