First point, related to the Cookie Consent, the law is clear concerning which cookie are exempt from any consent. One type of exemption is for the "user‑interface customisation" (source). I consider the resolution to be used only for customization of the interface and nothing else. As the product is open-source, you can check yourself that the resolution is never used for any other objective. From my PoV it comply completely to be put in that category and so, do not require any consent.
Second point, related to the GDPR, the definition of what is personal data :
"‘personal data’ means any information relating to an identified or identifiable natural person (‘data subject’); an identifiable natural person is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person;" (source)
As you may know, the resolution distribution among the population is somewhat standard and cannot be used to strictly identify someone. So from my PoV, there is no reason the screen resolution is a personal data or an information usable to identify the person.
If you find something else that could be impacted by the GPDR or are not convinced by my arguments, just tell me.