consmall signal block diagram
The context is not clear to me but the result can be arrived at by simplifying the block diagram. I have removed unrelated branches as well as some feed forward blocks to show only the two relevant loops; one of which is opened for finding out the open loop transfer function. The loop opening point is the \$\times\$ symbol seen near \$T2\$.

The inner loop can be simplified as \$\frac{F_m}{1 + F_m F_i F_4} = \frac{F_m}{1+T_i}\$. [Wikipedia]
Then the gain of the cut loop becomes \$\frac{\color{red}{(-1)} F_m F_2 F_v}{1+T_i} = \frac{\color{red}{(-1)}  T_v}{1+T_i}\$. When writing the open loop gain of negative feedback systems the negative sign shown above is implied and not actually written down.
When analyzing the stability of the given loops, the feed forward terms such as F1, F2, F5 etc. are not relevant.