Um, I'm speaking under correction, but many mice from the 1990s were dual mode, no matter their connector.
The chips inside did understand both the RS-232 and PS/2 protocol equally (MS Mouse). All it needed was a mechanical adapter.
That's because the RS-232 interface of Microsoft compatible mice was a hack, anyway.
Some of the status lines were used to power the mice and/or for communication. Not RS-232 conform, as such.
Again, speaking under correction. PS/2 vs USB is another story. But RS-232 mice and PS/2 mice used similar technology.
Edit: Ah, I understand now. You want some sort of protocol filter/translator for your mouse. So you can use standard drivers.
That's definitely possible, but I'm not aware of something like that.
You can try converting up and down, however. Use multiple converters in a chain, so to say. Serial to USB and USB back to PS/2 or serial..
Not sure if such mouse converter projects exist, however.
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