I got the same problem like this guy -> https://stackoverflow.com/questions/61383959/typo3-fal-in-flexform. So I used this answer but I have some problems to add the data processor. At the moment I render the Element like this:
tt_content.gridelements_pi1.20.10.setup {
1 < lib.gridelements.defaultGridSetup
1 {
prepend = COA
prepend {
  10 = TEXT
  10.value = </div><div class="bg-img-section">
  20 = IMAGE
  20 {
    file {     
      import = uploads/tx_gridelements/
      import.data = field:flexform_image
    }
    dataProcessing {
      10 = TYPO3\CMS\Frontend\DataProcessing\FilesProcessor
      10 { 
        references.fieldName = image as = image 
      }
    }
    stdWrap.wrap = <div class="image">|</div>
  }
  30 = TEXT
  30.value = </div><div class="inner">
}}}
There is no Image shown in FE. I really tried to fix this on my own, but I just couldn't find a solution. I would be very grateful for any help or explanation