When attempting to make custom splash texts for my resource pack, I discovered that strikethrough does not show up in game. The rest of the formatting, such as color, italics, bold, etc. still works. Just not strikethrough. For example, in the photo provided, the "Bruh Moment" should be struckthrough.
I haven't tested whether strikethrough works anywhere else, like pack descriptions or anything, so I can't provide info on that.