Windows 10: 4TB external disk is shown as MBR formatted. How is this possible?

The reason for my question is as follows.

I had a 4TB Samsung D3 Station external disk that suddenly stopped working. I determined that the problem must have been with the external enclosure and I therefore bought a replacement. Upon trying to connect the drive Hard Disk Sentinel reported that "the partition on this hard disk created (sic) with 4K physical sector size but the current physical sector size is 512 bytes" and "it is recommended to re-connect the hard disk as previously connected (probably with different USB adapter, enclosure, docking station or so to access the partition with ll stored data - otherwise data loss may occur".

To cut a long story short, I eventually reformatted it as the data on it were already backed up elsewhere. However, I ended up with two partitions and I couldn't merge them, apparently because the size of one of them exceeded 2 TB. I finally used a program from AMOEI and I created a single partition on the disk, equal to nearly 4 TB.

The partition now is GPT type. However, the previous partition on this disk, also 4 TB, was type "Basic MBR". So how come it was 4 TB Basic MBR in its original (new) form whereas I was restricted to partitions below 2 TB later on when I wanted to have a single MBR type disk up to 4TB? Does it have anything to do with the enclosure, that is the original enclosure from Samsung compared to the new enclosure that I bought?

:)