Why is partitioning not active during installation?

Question

Windows

I wanted to install ubuntu 18.04 next to windows 10, I followed the guide, the discrepancies with the guide began at the time of installation:
1) There is no installation option next to windows10, like this:

2) The "plus" is not active for creating partitions in self-creation. (The screen is not mine, but the plus is not active like that. Neither plus, nor minus, nor change. And all this is on the "free space" that is created if you bite off disk D, and it does not matter using windows tools or directly during installation.)

I rechecked several times, everything strictly coincides with the guide, but the "plus" is not active in any of the attempts.
Partition scheme: MBR

Answer 1

Either there is no unallocated space on the disk, or 4 main partitions have already been made.
I'm right?