Am i blocked on sms?

Hi I can’t tell if my texts are getting through. I first message was an iMessage and nothing underneath; no “delivered” or “read”. When I clicked on the iMessage I got and option to “send it as text” so i did. I know that doesn’t mean they received the text. I did a test with my sister & had her block me. When I looked at her info and the “send read receipts” toggle was gone. When she unblocked me it was back. Is this a reliable way to tell if you’re blocked? Also, is it possible to be blocked on iMessage but not sms & how do you tell? Btw we all are using iPhones.

thanks in advance!