Some terminals probably scroll sideways, but this `st` program seems to require running to completion. So, ^C does not give you any report at all.
While it does RSS not Proportional Set Size (PSS) { arguably parsing /proc/PID/smaps_rollup should be added } and does not integrate program launch with tracking or use netlink to track making kids, an alternative that might interest some is a scrolling terminal kind of log report out of the Nim https://github.com/c-blake/procs .
pd -pBHd1 -f "%N %R % %J %a" $(pf firefox)
or launch the program with `prog &` and use the shell `$!` to specify the PID or add -D'RJ' to get differential reports (or many other things). On the plus side, this can track many other things besides just memory & kids { like IO in the above example, assuming your Linux has /proc/PID/io support compiled in }.
You could always capture the output and feed it to some plotting program.