Accessibility issues with the Underline button in CKEditor

Issue

When using CKEditor, there is an underline button available. If you use it, the text will be inserted within u elements.
This fact causes some HTML validators to report an accessibility issue based on WCAG SC 1.3.1.

The u element is a valid HTML5 tag and was intentionally reintroduced into the standard.
If the tool you use is giving an issue there, it is likely to be a HTML validator, which are no longer relevant and were deprecated in WCAG 2.2 (SC 4.1.1: Parsing (Obsolete and removed). This removal affects all versions of WCAG 2.X. A note was added to this criterion in WCAG 2.0 and WCAG 2.1:
- This criterion has been removed from WCAG 2.2. In WCAG 2.1 and 2.0 this Success Criterion should be considered as always satisfied for any content using HTML or XML.
Regulation updates were made to avoid these types of reporting issues that in some cases blocked a healthy way of working on the positive and tangible impact of accessibility.
SC 1.3.1 is not a manual review criteria, it is an automatic validation by accessibility tools and there is no known way to get 1.3.1 error by using u and accessibility validators like AXE, for example.
The only one way to get the error is by using certain HTML validators, and there is where the SC 4.1.1 applies. It explains that HTML and CSS validators are not longer needed, if you are getting an HTML/CSS Error it will always be considered as satisfied.

As a company, we are committed to making Liferay an inclusive, accessible product that leaves nobody out. If you could provide a standard way to get this error and not rely on manual review, biased interpretation, or interpretation of outdated regulations, we would categorize that as an accessibility issue.

Furthermore, you may want to teach your content creators to avoid its use. This is because underlining text is not a recommendation since it is normally reserved for links, so it can be confusing for all users.