Maximum capacity M2 SATA drive for Dell Inspiron 5570 laptop

Anything currently available will work, but bear in mind an M.2 SATA drive is a dead end purchase -- it won't be useable in any future system, since SATA is obsolete at this point.  I would carefully evaluate the cost of a higher-capacity drive against the length of time you plan to continue using the system.

I already have a Samsung 1TB M2 SATA drive available for this system that I already purchased.

I didn't want to install it until I'm sure that it will be compatible with this laptop.

It will work fine.