@Delwyn3I hope you are well!
To answer your question: I feel it's a reasonable request, and it's good hosting.
I ask the same of my self check-in guests, most do let me know when they've made it into the listing- but equally some do not.
I think it could be anything from having arrived not feeling the need to keep an eye on the Airbnb app, tiredness, jetlag to overexcitement!
If I don't hear from them on the day/evening of check-in I send a message the following morning to see if they had a comfortable first night, and sometimes they don't reply to that either.
I work on the assumption that if there was an issue or they weren't having a good time they most certainly would let me know about it!
I have trained myself to switch off from thinking that not hearing from them means they aren't having a good time or they didn't arrive.
If you host remotely and you want to see when guests arrive, and have some visual control at the listing you could think about installing a camera doorbell so you can see when guests arrive/depart- and you don't have to rely on their messages.
If you decide to do that, make sure you make it clear that you have a camera doorbell in your listing so guests are aware.
Paul 🙂