Looks like another PSE type test using blood biomarkers, PSA, etc. The UK NICE (part of NHS) writeup is almost 4 years old. It lists a 350 pound price for the test. The other reference one may be from the biotech that is trying to market the test. Text below is from that site.

Stockholm3 is a blood-based test that integrates protein biomarkers, genetic risk profiling, and clinical data to assess a man’s risk of harboring aggressive prostate cancer. Stockholm3 has been evaluated in prospective and population-based screening studies with a total of more than 90,000 men. In a European screening cohort (N=12,670), Stockholm3 has showed 90% sensitivity and 89% specificity for detecting aggressive prostate cancer (Grade Group ≥2 cancer). PSA ≥3 ng/ml showed 74% sensitivity and 90% specificity, while PSA ≥4 ng/ml showed 52% sensitivity and 95% specificity in the same cohort.[15, 16] Stockholm3 has been shown to enable detection of aggressive cancers while reducing unnecessary biopsies in men with elevated PSA levels compared to PSA-based referral pathways.[15-18] Long-term follow-up from the population-based European STHLM3 screening study suggests that cancers identified at low PSA levels but elevated Stockholm3 scores may be biologically aggressive and clinically meaningful. Men diagnosed under these conditions had an approximately ninefold higher risk of high-risk biochemical recurrence (an indicator of progression to metastatic and potentially lethal disease) after curative treatment compared with men with higher PSA but low Stockholm3 risk (HR 8.8; 95% CI: 1.06–72).[14]
https://www.stockholm3.com/usa
The UK reference from 2022 about this test:
https://www.nice.org.uk/advice/mib303/resources/stockholm3-for-prostate-cancer-screening-pdf-2285967566184901