I have been using Premiere Elements bundled with photoshop element for more than twenty years with various version, 7, 11, 14, 18 and now 2021. I always encountered bugs and been able to go around them to finalize my videos. This time no rendered (rendus) possible on my MP4 included with my photos. Of course, impossible to export the video. I had to eliminate all the videos, registered the video, exported in MP4 and use my previous version (18) to rintroduce the videos in the spaces left empty. I did the (rendu), registered and exported the entire video all inclusive. I can not believe that we still this kind of problem after all these years on the market. And we pay each time more than a hundred dollars for these unfinished products. Noone reviewing theses software before selling them? To say the least, I am not happy after all those hours passed to find a solution. Don't tell that people have different configurations and computers. I used the same computer. No change! You should First concentrate on having a final product of a perfect quality instead of adding the small amount of improvements to launch an unfinished product. I use the french version. Not downloaded but purchased in store. And try to improve your communication system as well. Thanks.
This is a user to user forum. If you have a complaint about the product or you want your money back you should contact Adobe Customer Care. They are usually quite helpful when it comes to providing refunds and addressing issues. You can contact them via Chat at https://helpx.adobe.com/sea/contact/what-contact-options.html
If after that you'd still like suggestions for troubleshooting your issues, we are glad to help.