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I would recommend checking out LosslessCut. Behind the curtain it runs ffmpeg, so you should be able to find the perfect command.
In the features list:
View ffmpeg last command log so you can modify and re-run modify recent commands on the command line
I would try the -to option with a negative duration. (I'm assuming negative duration counts from the end of the file instead of the beginning.)
I think this is the easiest. But, -to can't do negative times. You need to nest a different comment inside the FFmpeg command to to the math.
I think this might work to remove 2 seconds from the end of a video
ffmpeg -ss 0 -i in.mp4 -t $(( $(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 in.mp4 |cut -d\. -f1) - 2 )) -c copy out.mp4
This is my (controversial) tip: ask an LLM. It works wonderfully for these cases. "Give me an ffmpeg command that cuts the last X seconds of a video in a lossless manner, stabilizes it and speeds it up 200%".
You can then checkout those commands on the manual/online to verify.