Can I put a .mp4 in a .m2ts timeline?

I am re-editing s project I did in 2019.
Problem is my laptop crashed last spring but i did find an external with the edited .mp4 files and the original .m2ts.
I put the .m2ts on the timeline just fine but when trying to put the .mp4 on a line above it i only see the .mp3 audio files showing up and nothing for video.
The client only has the .mp4 to edit from and I do not remember the original edits that were on the laptop that crashed...so I want to compare the original .m2ts files with the dited files and his new edits...and there is my problem.
Maybe there is another way of doing this I am not getting.
My other option is to edit the .mp4 but I am sure it will degrade the video for his new product.
Ideas...Suggestions?

Thanks!
Mark