Here's OP's tard script converted to an actually useful bash one where you don't have to rename every input file to in.mp4 lol. Also added 2-pass because VP9 being a google frankenstein video codec, "b-frames" will NOT be generated with just 1 pass.

>-auto-alt-ref <int> E..V....... Enable use of alternate reference frames (2-pass only) (from -1 to 6) (default -1)

#!/bin/bash
for f in *.mp4; do
ffmpeg -i "$f" -c:v libvpx-vp9 \
-pix_fmt yuv420p -auto-alt-ref 6 \
-b:v 0 -crf 30 \
-cpu-used 0 -aq-mode 2 \
-tile-columns 1 -row-mt 1 \
-pass 1 -an -f null -

ffmpeg -i "$f" -c:v libvpx-vp9 \
-pix_fmt yuv420p -auto-alt-ref 6 \
-b:v 0 -crf 30 \
-cpu-used 0 -aq-mode 2 \
-tile-columns 1 -row-mt 1 \
-pass 2 -an "${f%.mp4}.webm"

done

I personally use picrel for windows but it's pretty fun being able to do computer stuff on your FFFUCKING TELEPHONE.

Crazy how all the fucking VP9 shit is just this with AV1:

ffmpeg -i "$f" -c:v libsvtav1 \
-preset 5 -crf 40 -pix_fmt yuv420p \
"${f%.mp4}.webm"

so clean, so short, beautiful