Unable to upload images - call to undefined function strlength()

-- url of the page with the problem -- : kaixo-design.de
-- HikaShop version -- : 4.7.1
-- Joomla version -- : 4.2.7
-- PHP version -- : 8.0.26
-- Browser(s) name and version -- : Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0
-- Error-message(debug-mod must be tuned on) -- : "Call to undefined function strlength()" If choosing an image from the repository

If trying to upload a image the progress bar ends up showing 100%, but turns to red.

Hikashop refuses uploading image, nevertheless I try to create a new product or edit an existing one. It always ends with a red progress bar or, when trying to select an existing image, with call to undefined function strlength()

Thank you for this very fast reaction. I'll do a backup before, but is there any risk loosing my hikashop content and/or configuration when I install hikashop over the existing system?

Thank you for clarification, Nicolas!

Solved!