I also added a photo of a widget within Chrome scaled. Anyone knows how can I correct this? Thank you in advance.
In Discord's User Settings you can change the "Zoom Level" of the whole window under "App Settings > Appearance". cmd+ and cmd- can also be used to change this Zoom level.
cmd0 is meant to set it back to default.
If I am understanding you correctly one app seems larger than another app?
Unfortunately it is not possible to adjust the resolution for an individual app. On macOS (and Windows too) the resolution of the screen is set on a screen by screen basis and can't be set for a specific app.
In System preferences > Displays
You can adjust those parameters.
If you have more than one display you could adjust the resolution on each display and keep those particular apps on the screen they look best on.