If you are remoted into a computer and the view has black bars on the top, bottom, and/or sides of the screen, the aspect ratios and/or resolutions of the local and remote machine do not match.
To resolve this issue, make sure both the local and remote computers have matching display resolutions. Configure the display settings on each of the local and remote computer's operating system and have their respective resolution size match each other.
1. Open System Preferences > Displays > Scaled > In box "2", the display resolution can be adjusted
2. You can also check the screen size and maximum resolution of your current Mac system
1. Right-click the desktop background and select "Display settings"
2. Select the correct monitor you would like to configure if you have multiple monitors
3. Left-click the resolution size and select the appropriate resolution size that will fit the remote session screen
If these configurations don't resolve your screen size issue, the local and remote computer monitors do not match and you will need to have both monitors each on the local and remote computer have the same aspect ratio.
Link to match aspect ratios and resolutions: https://the-wallrus.com/aspect-ratio-and-resolution/