This came up a few years ago when I was doing a Union Rep training course.
If you are not going in to work because you are too ill to work, your responsibility is to let school know, asap & via whatever channel is school policy. That's it.
You cannot be expected to set work or do anything else work-related, because you are Not At Work because you are Not Fit For Work.
In the real world, if I'm off because say I've broken a couple of ribs in a Lego-related incident, as last year, there's obviously no reason why I can't email in work. It's better for the students, less hassle for whichever colleague otherwise has to sort it out, & means it's easier for me to pick up the pieces on my return.
My school has a culture/expectation that, in a spirit of professional goodwill, you provide as much in the way of lesson suggestions as you possibly can - I've emailed confused ramblings before now whilst self, dh & 3dc were all riding the Norovirus train...
However, it cannot be a requirement. You can't be reproached for not sending in lesson plans etc, because as soon as you've let school know you are too ill to work...you aren't working.
Really, any decent Department should be able to provide one day's worth of acceptable cover work. We have an electronic folder for each Scheme of Learning - it's mostly scans of slightly dated worksheets, & topic-related videos, but it creates a breathing space so that if someone's going to be off for several days, another member of the Dept. can then plan the next few days & liaise with the supply teacher.