Blocking sunlight is one way of slowing down the warming but reducing the sunlight will also reduce the productivity of photosynthesis which will reduce crop yields among other things.
It doesn't matter if you do it at times when plants are getting too much sunlight, which already happens. You can tell they are getting too much sunlight because either a) it is over 100 degrees when virtually all plants close down their stomata and just try not to lose all their water and die or b) the plants are literally getting sunburned, which is also a thing which happens.
Also it doesn't do a thing to stop ocean acidification.
That's true. Also, we have to breathe whatever comes down, and there's basically nothing whatsoever which is actually safe to spray up there which will also do the job.