title: TYPO3 9.5.x feuser with uppercase letters
body: <p>I want to allow upper case letters for frontendusers in TYPO3 9.5.x.
  When a new feuser self-registers via sfregister_form, it works, but when I add a feuser in the backend, the username gets converted to only lowercase letters.
  I found solutions here in the forum <a href="https://www.typo3.net/forum/thematik/zeige/thema/47903/" rel="nofollow noreferrer">https://www.typo3.net/forum/thematik/zeige/thema/47903/</a> how to (propably) change it, but they only work in older versions of TYPO3. Since there has been lot of changes in TYPO3 since the 10 years old post and I found nothing that talks about TYPO3 9.5.x I ask the question here.</p>