There's no way around it. You have to sanitize the images URLs. I've written a python script to remove non-alphanumeric characters from the full path of each image.
Also, this version of Magento limits the image name to 90 characters by default. Some posts show a workaround for that.
I don't know if you fixed the problem, but I will post my solution in case someone else has the same problem.
I encountered the problem with Magento 2.3.5-p2 with PHP 7.3 and Firebear/ImportExport v3.1.6. I think that the main issue is that the extension versions below 3.2.0 are not fully compatible with Magento 2.3.2 onwards as it's stated in the ...