I don't get why it's not ok to steal food from a grocery store but it is ok to not pay rent. Both are basic necessities and in both cases you hurt someone else by not paying for service (food/shelter).
I'm sure there's a moral framework where it's never acceptable to hurt someone else when you could sacrifice yourself instead, but I don't think that's a particularly common school of thought. More often people will weigh two potential harms to make a decision, like "I can't pay my rent, but property taxes and foreclosures have been suspended during the pandemic, so my landlord will likely suffer less harm than I would if I became homeless."
Finally, "can't pay the rent" doesn't necessarily mean silently fail to mail a check. It might mean talking to the landlord about a payment plan, or frankly telling them you have no money and can't even afford food for the week. Landlords are humans, just like grocers who might give food to a starving person
To paint landlords as rentiers who can easily afford to go without rent or with greatly reduced rent is wrong. It mischaracterizes the problem in a way that will lead to bad solutions.
If there is to be rent reductions or forgiveness, there must also be reductions, aid or forgiveness on mortgages, property taxes and utilities. Somebody needs to pay for these things. Yes, profits will be reduced, but losses cannot be sustained for as long as social distancing measures are expected to last.
[1] https://www.huduser.gov/portal/pdredge/pdr-edge-frm-asst-sec...
That said I agree there are many edge cases in this crisis and that, ideally, assistance should be given fairly liberally to all individuals who find themselves in tough situations.
I can afford to pay my rent. I have no problems doing so. However, if I were to learn that my rental management group were facing a large rent rebellion, that I believed that the rebels had legitimate complaints, and that the rental management group could survive the rebellion by evicting all of the rebels but only if I paid my rent, then I would consider not paying my rent.
Therefore, I can imagine a situation where I would not pay my rent despite being able to afford it, and be expressing solidarity by doing so.
I don't really care whether or not you're sympathetic right now to this particular cause, but you should consider the principles behind the actions that people are taking, and spend some time putting yourself in everybody else's shoes.