PREMIERE PRO VERSION BELOW
If you have shifted through the jerry springer script (the one between the "true" story tellers and the "gimmicky" filmmakers, that is exhausting and a well-rounded waste of time) and got to this part, I have included a preset for adobe premiere pro (cc 2018) that does much to replicate this effect without leaving and dynamic linking. It isnt exact, and I would recommend combining it with Tiffen dfx's widescreen a little bit, simply because people are not wrong it is a combination of the vertical perspective and the wideness of the lens (why it doesnt work so well once you use lenses past the 35mm FF length) but wanted to make sure the preset was useable by all and only contained the default effects and tools necessary. Please note that one will probably have to unclick uniform in their motion panel of effects and, while keeping the length and width .4 or .5 pixels close, scaling their footage to where it covers the curved outline of the corner frame.
That, or you could just use letterboxes. But that defeats the whole purpose since youtube allows 21:9 in all its widemouthed glory to be displayed without those black bars hogging up real estate.. also please note the preset was created with 3840x2160 in mind, but can easily be adjusted for anything beyond 16:9
For the record, Vashimorphic helped me a ton with wedding filmmaking. I don't use it for commercial clients, but for epic weddings brides love it.. example here, shot with 17.5mm voigtlander (35mm on gh5): https://www.youtube.com/watch?v=6n0nD8hTOIs