Parsec by default allows you to connect to resolutions in standard 16:9 aspect ratios like 1920x1080.
If you have a display on your client machine that is in a different aspect ratio than 16:9, this may result in black bars - to fix this, please follow this guide here.
Custom aspect ratios and resolutions are only possible on Paperspace P5000 and P4000 cloud machines.
1. Connect to your P5000 / P4000 cloud machine and right click on the Desktop
2. From the NVIDIA Control Panel navigation tree pane, under Display, click Change resolution.
3. Select the icon which represents the display monitor you wish to affect (there should only be one)
4. Click the "Customize" button to bring up the Customize window
5. You will be unable to create a custom resolution, but there will be one available already
6. Click the "Green Pencil" button
7. Set the custom resolution you require - normally the resolution of your client monitor (Important note: Be careful - if you set this too high - like 5120 × 2880, or at a very obscure number, you may not be able to reconnect to the machine).
7. Click on the "Test" button which will cause the graphics card to query the display and verify the new custom mode is supported. If not, the test will fail and you will not be able to add this new custom resolution
8. Once the custom resolution has been successfully added, you will be able to click OK to close the Window, and select the resolution in the NVIDIA Control Panel
9. If the resolution you set matches the client displays resolution, you can open Parsec settings and make sure "Autodetect" is set and Parsec SHOULD by default select the new resolution, if it does not, you can select it via the NVIDIA Control Panel when connected to your P5000 cloud PC