welcome to the community @tkd 
I don’t really get the problem… there must be some issue with mount points but you didn’t describe what is the exact problem.
Another “problem” is you are using linuxserverio container image which has it’s own spetialities - if you prefer this for a reason I would recommend you reach out to linuxserver.io Support and linuxserver.io Nextcloud docs
If you consider a “standard” Nextcloud community image look at this guide I posted shortly Nextcloud docker-compose setup with notify_push (2024)
aio is a good option to start as well.
your mount points look little weird - /nfsvolume1 likely doesn’t exist and never used in the container… I’m not sure how linuxserverio handles this - using community docker you would map not only config but apps and data as well.
In general I would not recommend to map existing NAS share as Nextcloud primary storage. Nextcloud is designed around an assumption it has exclusive access to the storage and doesn’t work good when you temper with the storage outside Nextcloud.
but you can definitely map the /nfsvolume1 into the container and mount it as “local external storage” so you can access files on the share as well…