Maybe someone knows good apps or programs for cell phones / laptops for editing short videos? (preferably free)
Get videoleap, super features and free, especially for editing:-)
I recommend daVinci Resolve for the computer and Enlight Videoleap for the smartphone. Both very good, free programs.
I use Shotcut.
https://shotcut.org/
https://shotcut.org/howtos / getting-started / Erste_Schritte_mit_Shotcut.pdf
Otherwise DaVinci Resolve is good too.
https://www.blackmagicdesign.com/de/products/davinciresolve/
Hitfilm Express is excellent software for your intentions and it's free.
Sorry that shouldn't be an answer to you…
Hitfilm Express is excellent software for your intentions and it's free.
I can also recommend Shotcut. I also use it and am very satisfied.
Shotcut if you need more features Kdenlive.
I can only recommend Shotcut. Use it yourself and it's going great.