In Windows, you can right click on an MP4 file, ensure it's not set as read only (uncheck Read Only->apply if it's set), then click the details tab. At the bottom of the details tab there is a clickable option "Remove Properties and Personal Information." Click that then select the "Remove the following properties from this file" radio button and check Title (and any other properties like Comments that you want removed" then click Okay. This process will remove the title property from .mp4 files.
For MKV you can use mkvpropedit like you've been doing, but in powershell you can do it recursively for all files. I use Plex, so my Movies dir has a child dir with the title and year, with the mkv and related files in that child dir. With this script you only have to point it to the Movies dir and it will recursively clear up the title attribute on all of the mkv files in all of the child directories (Obvs, be sure to change your -Path to the root dir where all your media files exist):
get-ChildItem -Path "D:\movies\" -Recurse -Filter *.mkv |
& “C:\Program Files\MKVToolNix\mkvpropedit.exe” $filename -d title
Hope this helps anyone who landed here after a google//Duck Duck Go search!