Hair nor beard do not help if geometry, perspective, colorfulness nor light do not fit.
A shadow on the collar is inserted. It's the masked curves layer.
The saturation levels on the head and suit are adjusted.
The collar must be wider for thicker neck. It's warped. The long nose must be near, it cannot be in the background. Heavy spherizing is applied to ...
As a professional I have access to Photoshop, so in this answer I use that, but you could use the same approach in a free alternative like GIMP.
Here we have an image in 700 × 400 px:
Then we first scale the image down to half size, 350 × 200 px using Automatic interpolation:
With this result:
And then we scale it up to the original size using Nearest ...