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I can confirm that there's no problem here (Debian 11).
Pretty sure it is an issue at your end. I have no clue about modern Windows. Probably something is blocking network access. Some other threads about the same problem:
Hi,
I recently installed QuakeInjector on a newer computer. It's Windows 11 now, but I tried in Feb as well when it was Windows 10 and got the same thing. When I open it, it says "Failed to fetch current database." Any tips? Thanks.