I have been using Adobe Media Encoder 2021 to render my After Effects (2021) videos. I have had no issues, and have had the choice to switch the videos from MP4 files to MP3 files when i feel necessary. For some reason though, as of yesterday, every after effects project i put on Media Encoder shows as an MP3 file and wont let me change it. I have been have to use handbrake again to render which is extra work. I hate that this has worked perfectly for me for months and now all of the sudden it isn't even something I can use. I use a Macbook air 2017 and doubt it's an issue with my computer. I have attached a photo of what all of my files have been looking like when i put them on Media Encoder.
Click on the Format pop-up menu (set to MP3 in your screenshot) and change that to H264 or HEVC (H265). You will then have MP4 presets in the Presets pop-up menu.
unfortunately that isn't showing as an option. It used to, but now MP3 is the only option for my files.
Use Creative Cloud Desktop to uninstall and then reinstall Adobe Media Encoder.