Single-core performance is generally very important because much software is not fully parallelized to use multiple threads. Increasingly, Web Apps are replacing traditional platform-specific compiled binaries, yet Web Apps are inherently single-threaded. It could take many years until languages and frameworks are improved to harness multi-threading on Web Apps. Until that happens, only improvements to single-core CPU performance will make those run faster.
FCP is significantly multi-threaded, but some workloads still run mainly on the main thread. Thus, only faster single-core performance will improve that.
You did not state the version of your Mac Mini, nor the version of GeekBench. You can't compare, say, GeekBench 5 to GeekBench 6. But even within a major version number, it's best to use the exact same version on both machines.
If your Mac Mini is an M4, it's fully expected the single-core performance is faster than any version of M3 (including Ultra). The M4 micro-architecture was significantly improved to produce better IPC (Instructions Per Cycle). Within a given generation of Apple M-series chip, they use the same micro-architecture. In general, the single-core performance of M1, M1 Pro, M1 Max and M1 Ultra are about the same. Likewise for M2-series and M3-series. The single-core micro-architecture was tweaked from M1 through M3, but M4 was the first big change.