Formatting Large Bars/Measures

I assume when you say you "attempted to format" you mean that you reduced stretch (select range that you want to fit and use shortcut "{" repeatedly). But this might not be enough to make so many notes fit on one line if they're too big. Change the staff space value to make everything smaller (Layout -> Page Settings -> Scaling).

Sometimes you can slightly alter the Traliing Space etc. of the notes particularly where only parts of your score have long runs of many small notes.

For really complex bars I find it easier to split them into chunks such as 8/4, 8/4, 2/4 then hide the barlines in the middle. A combination of small notes, fiddling with the Trailing space and shorter stretch is needed.

For your extreme example you really need to go all out and make the notes small, set a Trailing space of -0.3 and be very careful with the accidentals.

[Edit]
I've added an extra sharp into the Key Signature to allow you to experiment in getting all the accidentals correct (actually I just did it by mistake but cannot face changing it now).

I've had exactly the same problem. I had a huge cadenza in a piece Variations_Concertantes_pour_Chant_et_Violon.mscz which required 54 beats in a 4/4 bar, as well as other sections of florid ornamentation which stretched the bar sizes. Musescore lets you enter something like this but falls over handling the page formatting. Obviously this is not an issue in a handwritten score from 1840, but as you said, the bars disappear off the side of the page into nowhere.
I'll try breaking it down into sections and hiding the bar lines, but there has to be a better way I think.