i've been using putty (in linux)
https://www.putty.org/
but that it doesn't seemed very feature rich (at least in linux)
to toggle DTR/RTS signals, i think those are literally 'usb' signals (i.e. usb cdc acm)
I think
stm32loader does that from within python, using (
pyserial), I think.
i think stm32loader 'ab'uses DTR/RTS signals to toggle reset and boot0, that saves having to toggle it manually.