You are right, Limesurvey LS 6.x is using jQuery UI 1.13.2, which was released in Juli 2022. So it is almost 3 years old.
However, I could not find any information about vulnerabilities of this version of jQuery. Do you have further information about which vulnerabilities and security issues are prevelant in jQuery 1.13.2?
My research gave me this:
security.snyk.io/package/npm/jquery-ui/1.13.2
Also, JQuery is not as frequently updated as Limesurvey and usually within the same main version of Limesurvey, dependencies are not changed as long as there are no known vulnerabilties in the script.
There have been only 3 releases since, link 1.13.3, 1.14.0, 1.14.1 (the later two in the second half of last year.
In any way, let's see if someone has more insights whether you can change to another jQuery.