There are 2 slots. The first is M.2 and takes either a 2280 or 2230 NVME/PCIe SSD. The second is M.2 and takes an M.2 2330 NVME/PCIe SSD.
1 TB would be the limit as Crucial always tests SSDs for compatibility and they only offer up to 1 TB. And I have checked other online retailers and no one offers larger than 1 TB, which leads me to believe that the system will not support and possibly not recognize any larger capacity SSD.