As worked out in another issue JuliaInterop/CxxWrap.jl#510 (comment) at last the Gecko products for Julia 1.12 need a rebuild due to some binary incompatibility. I have confirmed that rebuilding Gecko (via dev'ing gecko_jll) locally fixes the issue on my machine. https://github.com/JuliaBinaryWrappers/gecko_jll.jl states that I should open a bug report.
Please note that the discussion in CxxWrap suggests that there might be potentially more faulty products hidden in the artifact system .