Steps to replicate the issue (include links if applicable):

• Use an old browser Chrome version 64 to 81 (browserstack) or chrome in docker (see bellow)
• Open https://en.wikipedia.org/w/index.php?title=Wikipedia:Sandbox&action=edit
• Without changing anything, submit it as a no-op.

What happens?:

• You are redirected to the same page again with the error

Incorrect or missing CAPTCHA.

What should have happened instead?:

• You should see the hCaptcha challenge and be able to solve it and save the edit

Other information (browser name/version, screenshots, etc.):

• Chrome browsers from 81 to 64

Version older than 64 don't even get the js delivered (See https://phabricator.wikimedia.org/T178356)
Versions newer than 81 shouldn't have this bug.

Assuming your local web dev site is at https://en.mediawiki.localhost:8443

Run

docker rm -f old-chrome && \                                                                   
docker run -d --name old-chrome --network oldff \
  -p 5900:5900 \
  --add-host=en.mediawiki.localhost:host-gateway \
  --shm-size=2g \
  -e SCREEN_WIDTH=1920 \
  -e SCREEN_HEIGHT=1080 \
  selenium/standalone-chrome-debug:3.8.1

Then connect over vnc with password "secret": vncviewer localhost:5900

Inside vnc go to en.wikipedia.org to see the bug, of if you're testing this locally you can run from bash:

google-chrome \
  --no-sandbox \
  --disable-setuid-sandbox \
  --host-resolver-rules="MAP en.mediawiki.localhost 172.17.0.1" \
  https://en.mediawiki.localhost:8443/wiki/Main_Page

After you're done testing: docker stop old-chrome