uploading pictures from the module uikit gallery does not work. Gives error. Uploaded pictures after uikit gallery was installed are not visible! How to solve?

using joomla 4

Not enough information.
Which Joomla version (exact specification) and which PHP version is used?
What error message does it come up with? Screenshot please.
Are images uploaded at all via the Joomla media manager in the media center?

joomla 4.2.5
PHP 8.0.15
Uploading via media manager joomla 4 also does not work I just noticed.
Also added this line to PHP.ini -> upload_tmp_dir=/home/vhosts/liliverde.com/httpdocs/tmp

OK, then it's not a UIKIT plugin problem, it's Joomla itself. Are the directory rights set correctly and do you still have enough free web space?

If I upload van JCE no problem and enough space. What directories have to be set different?
If I upload van JCE I can see the file in the folder with JCE but UIkit Gallery does not see the file!

There are many reasons. There is no specific directory for uploading the images for UIKIT. Check in the media options whether the image format is allowed and whether the upload size is set too small. Valid image file extensions (file types) and disable restricted uploading.

AND
Clear the Joomla cache and browser cache

Although the temporary directory was not set, there shouldn't usually be any problems. So you can ignore the notice.
Otherwise, your hoster can help you with this.