This is not about authoring the DVD (not similar to this question): just want to insert the DVD in a laptop, start it in a video player, and then add a separate subtitle that I have myself found. (Some DVD movies contain no subtitles - or some subtitles may be needed that are not on the DVD.)
I know how to do that in Windows and in Linux - without VLC: it can try but has bad results in this respect. - Every time I try it, external subtitle display for a DVD in VLC is erratic; usually subtitles are not always displayed, or they disappear after a while, namely after pause/play or after going back and forth. (See here, here, here, here about this old bug that is not yet completely gone, afaict.) Here it says VLC is the only Mac player that can do the job. But is it?
Are there some Mac video players that could achieve this task - like MPC-HC (Potplayer, etc) can in Windows (and MPV and SMPlayer in Linux)?