$$ \mathrm{Mn}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4 $$

$\mathrm{d}^4$ configuration in $\mathrm{t}_{2 \mathrm{~g}}$ and $\mathrm{e}_{\mathrm{g}}$ orbitals will always have unpaired electrons irrespective of SFL and WFL.

$$ \mathrm{Fe}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5 $$

$\mathrm{d}^5$ configuration will also have unpaired electron irrespective of SFL and WFL.

$$ \mathrm{Co}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6 $$

$\mathrm{d}^6 \Rightarrow$ it can be both paramagnetic or diamagnetic based on field of ligands.

In case of $\mathrm{F}^{-} \Rightarrow$ weak field ligand, configuration will be $\mathrm{t}_{2 \mathrm{~g}}^4 \mathrm{e}_{\mathrm{g}}^2$ hence it is paramagnetic but in case of $\mathrm{en} \Rightarrow$ strong filed ligand, configuration will be $\mathrm{t}_{2 \mathrm{~g}}^6 \mathrm{e}_{\mathrm{g}}^0$ hence it will be diamagnetic.