If multiple apps or single app attempts to decode multiple video files, what is the maximum limit of files a decoder can decode simultaneously?
Maximum limit of files to decode in iOS app
There may be a performance limit, which depends notably on the device processing power. It will also depend on the type of encoding, of video format (4K is not equivalent to Quarter Video Graphics)
If decoding is async, then that will result in delays in decoding.
So, there is no general answer to your question.
How many files of what type do you consider ?