Doom 4:3 has weird sidebars

[WafuRuns]

Doom is not the only game that has this issue, but some games just create these sidebars, it also doesn't seem to be possible to have it stretched to the full height of the monitor.

[DerKoun]

AFAIK the edges are cut off so there are less pixels to compute. So extending the view is not possible without hacking the game.
Up to beta 9 there was the soft-crop option. Using that old version you could ignore the black edges, zooming the image in to fill your monitor more.
Other games, that render in a more 'normal' way, can have sidebars removed by using the Ignore window setting [and in some cases BGn:crop(auto)].