Arduino serial plotter with independent Y axis, is it possible?
No. The Arduino Serial Plotter only supports one Y axis.

An alternative would be to capture the data into a file as CSV data and use some other software to plot it - you could import the data into Excel / LibreOffice, or (as I prefer for quick graphing) use something like GnuPlot (or whatever is similar for your chosen OS).

For instance, this is a GnuPlot configuration for plotting two independent axis datasets and the results:

set datafile separator ","
set terminal png enhanced size 1360,768
set output 'testCharge.png'
set ytics nomirror
set ylabel "Current (A)"
set y2label "Voltage (V)"
set y2tics nomirror
plot "testCharge.csv" using 3 smooth bezier title "Current" w l, \
     "testCharge.csv" using 4 title "Cutoff" w l dashtype 2, \
     "testCharge.csv" using 2 smooth bezier title "Voltage" w l axes x1y2


The data I use is formatted thus:

Phase,Voltage,Current,Cutoff
0,3.58,1.098,0.033
0,3.59,1.098,0.033
0,3.59,1.098,0.033
0,3.59,1.098,0.033
0,3.6,1.098,0.033
0,3.6,1.098,0.033
0,3.6,1.098,0.033
0,3.61,1.098,0.033
0,3.61,1.098,0.033
... etc ...


And the results:

Incidentally, that's me charging a Li-Ion battery and monitoring the voltage and current.