Beelink says 2TB for M.2 2280 NVMe, 2TB M.2 2280 SATA III and 2TB SATA III.
However, I bought a WD_BLACK 4TB SN850X NVMe Internal SSD (Gen4 PCIe, M.2 2280) for a desktop. I have tested the SSD in my GTR5 5900HX and it works great! I also have a 4TB Western Digital Blue SSD SATA III attached to the internal enclosure to save my backups and all is fine.
I'm still using the 4TB WD Blue for backup but took the 4TB WD_BLACK for my desktop (server)... 2TB NVMe is more than enough for my personal use on the GTR5 5900HX :)