I upgraded from Premiere Elements 2020 to 2021. In 2021, none of my files can be viewed anymore, although they were ok in 2020. Many of the clips are filmed on my Samsung S10+ or my Canon HDR camera. What is wrong? Are there codecs not compatible with 2021?
Did you open a project that you created in version 2020 with version 2021? That will not work and can cause project corruption.
Or are you saying that you started a new project in version 2021 and your videos do not play when you add them to your timeline? If so, can you post a screen capture of what you see when you try to play your timeline?