The rates in the Trading 212 UK entity are related to the Bank of England rates, this is what the T212 support agents have told me. I never said the euro rate is linked to the BoE GBP rate, which obviously is not. But the interest they offer for the UK entity it's not linked to the exact value determined by the ECB, and it's impacted by the BoE policies, fx conversion rates and money interest rates.
While obviously the ECB rate impacts the Euro rates in all jurisdictions, the actual interest rate T212 provides depends on more variables than just the fixed ECB rate. T212 does not tie its uninvested cash rates to the ECB interest rate the same way Trade Republic does, unfortunately for me, this is why they offer different rates in different jurisdictions, while the ECB rate is the same everywhere.
Hoping they will go up now with the recent ECB increase.