The problem is, that people do not update. Have a look at your version, it is 3.25.6+201229. That means that it was released at the end of 2020. Almost 3 years ago. There are far newer versions of the same LS3 branch.
The same for upgrades. A lot of organizations do not want to upgrade regularly. So older versions are still supported and receive bug fixes and security updates, but no new features anymore. Like LS 3 at the moment. It is supported, but it doesn't get any new features, just the necessary in terms of bug fixes and security updates, so that people who do not want to UPGRADE their version yet, at least can update it.
LS5 and LS6 are very similar in terms of features, the main change seems to be the new backend interface.
I don't see it as very confusing. This is a concept that also exists for operating systems (at the moment Windows 11 is the recent version, but Windows 10 still receives security support.
Same for different office versions.
Believe me, the Limesurvey team would prefer to have to maintain only 1 version of Limesurvey, but if they would stop supporting older versions once the newer version came out, there would be a lot of outcry in the forum.
You can expect the support for LS3 to run out soon. Then only LS5 and LS6 will be supported.
I answer at the LimeSurvey forum in my spare time, I'm not a LimeSurvey GmbH employee.
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