Just because an SSD is connected via M.2 does not automatically mean that the SSD is fast.
The 860 EVO M.2 uses AHCI (=slow) as data protocol and not NVMe (=fast). This does not show on an M.2. The 860 EVO Basic in the 2.5" version uses AHCI because it is connected via SATA data cable (max 560 MB/s).
Besides the difference in the data protocol (AHCI vs NVMe), the 860s also have slower memory components in order to be able to offer the lower price. Such storage is sufficient as a data grave, but you should not use it as a system disk with Windows on it just to save a few francs.

And be careful. Not all M.2 slots on mainboards support both protocols (AHCI and NVMe). You should therefore check before buying whether they can be used at all.