I agree with the opinion of others above that you are probably focussed on the wrong things from the experience. It can be frustrating when you don't get feedback, I have experienced this in the past and now I am an employer we make sure to provide feedback because we understand the importance of it. However you can be nearly 100% sure that there was nothing untoward or unusual or personal in not responding, some companies are just busy particularly when recruiting and feedback is not top priority or it can be an explicit policy not to provide feedback. The lack of feedback might just be an indication that the company wouldn't be a good match for as they may not be as people focussed as you expect.
I would suggest not to focus on it or that company and just move on to the next opportunity, keeping focussed and motivated will yield better results than starting a dispute with a company.
Regarding the queries on the the GDPR issues, I have done a GDPR Data Protection Officer course so I am more familiar with the regulations than most but not an expert so I thought I'd clarify some of the points from the little I know.
You can make a data access request and the company would be obliged to give you a copy of any personal information they hold in relation to you within 30 days as long as it is deemed a reasonable request. If there is anything that is confidential to the business or relates to third parties or deemed an inappropriate request then the company can refuse to supply the information. The refusal can be queried by the data commissioner if disputed but if the company has a valid reason (which may not be disclosed to you) they are deemed to be complying.
In this case you may end up getting your emails and CV returned to you but internal memos or emails maybe redacted. For example if an interview noted that they "did not think the candidate would suit the management style of X" or "Candidate X was more qualified than candidate Y" then that could be redacted because it relates to a third party.
The company could also deem that once an interview process is complete that the interviewee information is not relevant any more and is purged. Under GDPR companies should only hold personal information for a limited time and while it still has a business need. If they deem the information not to be necessary anymore then they may have permanently deleted it so there is nothing to be retrieved.
In terms of accessing the data from home or after hours, as long as there is sufficient security and protection taken in accessing the data that would not be an issue. Also the time of access should not be an issue too as long as it is being accessed for valid reasons and in this case there appears to be a valid reason.
Overall I think there would be little or nothing to gain from the GDPR Data Access Request other than reputation damage to you as others have suggested.
Best of luck with the job hunt!