I’ve gone from debian 9 to debian 11 and now debian sid without reinstalling OS on my desktop
Same with my servers. Debian 8 -> 11 all upgrades in-place. Will have to upgrade to 12 soon…
The only time i messed up an upgrade is when accidentally used the codename “bookworm” in the sources file and skipped a major version. The system tried to fully upgrade 2 versions ahead and promptly borked itself… But it was an LXC container so i just rolled back my mistake. Lesson learned…
But yeah. Full re-installs have NEVER been a thing for me since going debian. It will even happily clone to a new SSD when you need to upgrade your hardware. (As long as your new hardware has in-kernel drivers, or at least some basic functionality to boot and fix the problem, if any)