Permission problems nextcloud-data

I’ll start by explaining a bit. This is a system I made to store an archive of all the works me and a number of people have done for the past 5 years. We need to be able to access it at random times. Since this is connected to a 10gb connection, I also want to let people use the talk feature of nextcloud as an alternative to slack.

Got everything working except the storage. The PC configuration is a ryzen 5 3600x/16gb memory/ an SSD - and 2 internal HDD Seagate Ironwolf 8gb each.

This here is a screenshot with my problem and the configuration.

My operating system is on my SSD (has no backup except a manual one I do when i do updates) - and I wanted to keep the RAID HDD strictly for storage purposes.

I followed the guide here to setup my hdd RAID with mdadm:

I followed the guide here to setup nextcloud:

It all works except for the fact that I cannot write files to my external HDD.

This is my config.php:
There is no error in my apache2 log, so I won’t post that.

Now, please, if you do post an answer, and did read the entire thing - please think that I did try to play around with permissions as much as I could. The screenshots should be proof of that. If you do write a reply, please post what commands I should use.

Thank you.