TL;DR: can Veeam backup to QNAP ES's WORM shared folder and this be used as immutable storage (like Amazon S3) to protect against ransomware?

My boss tasked to find a solution for a customer for on premise backups. QNAP storage is the cheapest option (instead of having a proper server). Regardless of which on-premise storage used there is the issue of ransomware protected backups (e.g. air-gaped or immutable). For small clients we just use external drive rotation and someone at the site is instructed to switch the 4/8TB external disk every week. However, this is not feasible for 30TB. So what are the options?

• Using Amazon S3 immutable storage is an option (still waiting on Azure)
  • Con: but the customer wants to keep everything on premise and not be reliant on internet
• Using another air-gaped repository:
  • need a whole new repository - too costly
  • some finicky way to connect and disconnect it form network/power
  • ransomware can hit during its connected state
• I found this "WORM" NFS share function in QNAP ES (here for Windows and here for Linux)
  • Con: I can't find anyone on the internet posting about it that they used it and I cannot find any Veeam documentation on this feature

Anyone used or know about using Veeam with this WORM feature? Is there some critical disadvantage I am missing disqualifying this QNAP ES feature for ransomware protected backups?