neowin[.]net/news/microsoft-may-have-confirmed-build-22621-is-windows-11-22h2-sv2-rtm-release/
RTM means Release To Manufacturers -- once Microsoft feels that a new version of Windows is safe / stable enough, the RTM tag gets applied & manufacturers are free to start testing it on future products, getting their software packs together etc. It does not mean that Microsoft is done with this version by any means -- they'll continue to add updates, possibly features, and fixes right up until general release, *probably* October 2022. Version or build 22621 may also carry fixes for problems with the current Win11 release that couldn't be included in a cumulative update, e.g. something had to be rewritten instead of just patched.
TO get the 22621 ISO you need to be registered for the Insider program, which is basically just giving them your email address & checking a box or two.
insider.windows[.]com/en-us/
Once you're registered go here & sign in.
microsoft[.]com/en-us/software-download/windowsinsiderpreviewiso
If you'd rather, once you register you can switch a copy of Win10 or 11 to start receiving Insider builds, as long as it meets the qualifications for Win11. That way you'll get the new version & updates via Windows Update. You can turn off Insider builds in that copy of Windows whenever you want -- many do this once the RTM tag is official. Otherwise you can mount the ISO in Windows, double clicking setup to upgrade, with your choice to keep apps & settings or not. Or you can use the free Rufus to create a bootable USB stick with the setup files to install fresh.
