When the PS5 launched the M.2 slot was not yet supported, Now Sony has updated the system software to support up to 4TB in the secondary slot. The slot can fit M.2 2280 PCIe 4.0 SSD products. There is some room for a heatsink but most NVMe SSD offerings do not need one.
Adding 4TB to the PS5 would make gaming more enjoyable with more choices. Downloading games all the time can be tedious even with fast internet, The Samsung 980 Pro is available in up to 2TB and the performance is great. Sabrent has 4TB and 8TB M.2 SSD available.
The Xbox X|S use a different slot design that has not attracted much support.