AGI
Yes, in case of Firefox ESR you understood that correctly. I think the ESR version allows you to stay at a feature version for up to one year, yet still receive regular security updates during that time:
"Firefox Extended Support Release (ESR) is an official version of Firefox developed for large organizations like universities and businesses that need to set up and maintain Firefox on a large scale. Firefox ESR does not come with the latest features but it has the latest security and stability fixes."*
I am not sure if other browsers like Opera offer a similar version, you would have to check that.
And indeed there is something similar for Windows, it's called the LTSC Enterprise channel, and the 2021 version correspondends to 21H2 if I am not mistaken:
"It is a stripped-down enterprise operating system based on a specific version of Windows 10. Windows 10 LTSC don't have pre-installed apps such as Microsoft Edge, Cortana assistant, News, etc. Using the LTSC service model, you can delay receiving feature updates and only receive monthly device quality updates."
You would have to see if this version meets your requirements, but I think theoretically you could stay at a Windows LTSC version for up to 5 years and only receive security patches during that time. This could be an option if you suspect a recent large Windows feature update made a working system unusable for you and you would like to return to an earlier version.
https://learn.microsoft.com/en-us/windows/whats-new/ltsc/