Typically, the plugin folder only needs to be writable by your user account, but this could potentially vary depending on what user your web server is running as.
For example, most of my installs have the plugins folder set to 755, but this is because Apache is running as the same user as the owner of the folder. Check who your server is running as if you think the permissions are correct.
For more info on permissions and WordPress hardening in general, check out https://wordpress.org/support/article/hardening-wordpress/#file-permissions