Yes, access to the appstore will be enabled in case you want to install some apps that are not yet in your instance.
However, the ability to install apps carries risks, in the most extreme cases it may even prevent access to the server temporarily. In addition, one must be careful about the space available on the Nextcloud installation partition as some apps may require an amount of space that is not available in our instances (e.g. the Translate app). The advice is to contact us in case of doubt before proceeding.
Access to the app store can also be completely disabled: simply request this through your usual support channel.