I have exactly the same Problem and don't know how to fix...
Movie preview generation failed Output: {"0":"ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers","1":" built with gcc 10.3.1 (Alpine 10.3.1_git20210424) 20210424","2":" configuration: --prefix=/usr --enable-avresample --enable-avfilter --enable-gnutls --enable-gpl --enable-libass --enable-libmp3lame --enable-libvorbis --enable-libvpx --enable-libxvid --enable-libx264 --enable-libx265 --enable-libtheora --enable-libv4l2 --enable-libdav1d --enable-postproc --enable-pic --enable-pthreads --enable-shared --enable-libxcb --enable-libsrt --enable-libssh --enable-libvidstab --disable-stripping --disable-static --disable-librtmp --enable-vaapi --enable-vdpau --enable-libopus --enable-vulkan --enable-libsoxr --enable-libwebp --enable-libaom --disable-debug","3":" libavutil 56. 70.100 / 56. 70.100","4":" libavcodec 58.134.100 / 58.134.100","5":" libavformat 58. 76.100 / 58. 76.100","6":" libavdevice 58. 13.100 / 58. 13.100","7":" libavfilter 7.110.100 / 7.110.100","8":" libavresample 4. 0. 0 / 4. 0. 0","9":" libswscale 5. 9.100 / 5. 9.100","10":" libswresample 3. 9.100 / 3. 9.100","11":" libpostproc 55. 9.100 / 55. 9.100","12":"Input #0, mov,mp4,m4a,3gp,3g2,mj2