The subject says it all ; is that a problem that can exist ?

I have a toshiba T2130CT, that is in supposedly perfeftly working condition

I can hook a serial mouse on the com1.

But it does not work with a modem ( what I type doesn't appear, modem not detected by windows, etc )

Is that a problem that can exist, like, do mie use less pins than a modem, and so could one of the pins be desoldered and make it a partially working com port?

Or to the contrary, if a mouse works a modem should 100% work, if so what could I investigate ?

As I have multiple toshiba laptops of the same era, the modem & cable absolutley work ( USR SPortster ).

thanks !