TL;DR: Set SE_NODE_MAX_SESSIONS=<N> and SE_NODE_OVERRIDE_MAX_SESSIONS=true if you're running into timeout errors when starting a new session on Selenium 4.x.

I ran into an odd issue while trying to upgrade our Selenium containers to 4.10 from 4.0.1-beta, where our Capybara-based test suite would return Net::ReadTimeout that I narrowed down to tests that would use multiple sessions.

Turns out a change was made where the Selenium containers would limit themselves to a single session by default, so you'll need to set SE_NODE_MAX_SESSIONS to an appropriate number for your setup, and also SE_NODE_OVERRIDE_MAX_SESSIONS=true.

I still had some odd issues, but using seleniarm/standalone-chromium:114.0-20230615 worked, even though our CI is still amd64.

Good luck.