My experience with a similar camera lens protector on the S23U similar with your frustration. The constant need to open the cover for QR code scanning, especially with daily use of apps like PayLah and PayNow, is quite inconvenient. Nevertheless, it serves its purpose in safeguarding the camera lens, so it's a matter of balancing pros and cons.
I once purchased a cheap, off-brand case that offered integrated camera lens protection, eliminating the need to repeatedly open a cover for scanning. But this solution led to noticeable image degradation, also worst when the protecting lens got oily and surprisingly, dust still accumulated despite the closed design.
Also, my research indicates that some users have reported issues with NFC and Paywave functionality when using the Nillkin case, need open the camera lens cover for these features to operate correctly, is that true?