I used to be able screen record in QuickTime and save my recording as an .mp4 file through the export option. This gave me small file sizes that were instantly compatible with sites like Twitter... However, a recent update has made recordings exclusively "QT Movie" format, a much, much larger file size incompatible with Twitter and such.
The same recorded H.264/AAC encoded data at any given QTX resolution and quality setting is the same whether the data is stored in an MP4, M4V, or MOV container by a given platform and macOS combination. Unfortunately, it sounds as if your issue is more related to the default quality setting now built into the QTX player app itself—i.e., the player now exclusively defaults to the "Higher Quality" system encoder setting which has twice the video data rate of the "Greater Compatibility" setting which is now only accessible by the Finder's "Encode Selected Video Files" conversion feature.
I'm using HandBrake to convert from QT to .mp4 to get the files back to how I used to be able to save them. Does anybody know why it was changed or how to save recordings as .mp4 from the start with the new update?
As to why the MOV container is now "exclusively" used to store data, that is likely because it is generic in nature and may be used to store any compatible form of media data such as Apple ProRes422 (or HEVC) video or LPCM audio (now optionally available for encoding) while the MP4 container is normally associated "exclusively" with H.264/AAC content.
Basically, the changed default quality setting and A/V encoding features have mandated a workflow modification in your case because you actually want to downgrade your targeted output quality for posting on Twitter while Apple is more likely interested in improving support for archival editing and UHD features. Frankly, I consider your HandBrake solution to be your best current workflow option to reduce H.264/AAC file size. While you could use built-in macOS features to reduce an H.264/AAC file by almost half its size and manually change a file extension to MP4 if desired, HandBrake allows you to create either anamorphic or non-anamorphic files targeting a specific resolution, file size, data rate, or quality level and store it directly in an MP4 or M4V file container.
The above response assumes you are currently still exporting content as H.264/AAC MOV file content and have not switched to Apple ProRes422/LPCM files which are huge in size or HEVC/AAC files having increased resolutions and neither of which may be supported by Twitter. If you have accidentally switched to one of these compression formats, switch back and recheck the output file size and upload workflow. As to changing an H.264/AAC MOV file to an H.264/AAC MP4 file, simply change the file extension in the Finder or remux the data using an app like MPEG Streamclip or Subler. (This does not change the size of the file.)
