Operating System: Fedora Linux 40
KDE Plasma Version: 6.1.1
KDE Frameworks Version: 6.3.0
Qt Version: 6.7.1
Kernel Version: 6.9.6-200.fc40.x86_64 (64-bit)
Graphics Platform: Wayland

There are repositories for Fedora 38 and 39 but not for Fedora 40. 
I have added the repository for Fedora 39 but it does not work for Fedora 40:

$ sudo dnf install subtitlecomposer
Last metadata expiration check: 0:16:57 ago on Wed Jul  3 11:21:39 2024.
Error:
Problem: package subtitlecomposer-0.8.1-2.11.x86_64 from home_maxrd2 requires libavcodec.so.58.134()(64bit), but none of the providers can be installed
- package subtitlecomposer-0.8.1-2.11.x86_64 from home_maxrd2 requires libavcodec.so.58.134(LIBAVCODEC_58)(64bit), but none of the providers can be installed
- conflicting requests
- nothing provides libdav1d.so.6()(64bit) needed by libavcodec58_134-4.4.4-264.19.x86_64 from home_maxrd2
- package subtitlecomposer-0.8.1-2.11.aarch64 from home_maxrd2 does not have a compatible architecture
- nothing provides ld-linux-aarch64.so.1()(64bit) needed by subtitlecomposer-0.8.1-2.11.aarch64 from home_maxrd2
- nothing provides ld-linux-aarch64.so.1(GLIBC_2.17)(64bit) needed by subtitlecomposer-0.8.1-2.11.aarch64 from home_maxrd2
- nothing provides libm.so.6(GLIBC_2.17)(64bit) needed by subtitlecomposer-0.8.1-2.11.aarch64 from home_maxrd2
(try to add '--skip-broken' to skip uninstallable packages)