DRB split bearer by UE

Hello Experts,
As per this definition, is it mandatory to support the DRB split bearer by UE.
Can anyone please explain what does M indicate here?
As it is not mandatory to support by UE then what this M indicate?

Mandatory or not, my guess.

I think that M means this capability info you highlighted is mandatory to be present.
Not that UE is obliged to support this functionality.
So that bit can be 0 (UE does not support) or 1 (UE does support).
But it has to be present.

In the table of UE capability parameter in subsequent clauses, “Yes” in the column by “M” indicates the associated feature is mandatory. From 38.306.

Looks logical.

Definetely, that make sense.
Thank You!