Someone in my contacts list that used to have an iPhone has switched to a non-Apple phone, but still has a MacBook. So I want to be able to send this person messages using both iMessage and SMS.
To facilitate this, I split their contact in the Contacts app into two: one that contained the email address of their Apple ID, and the other that contained their phone number. This person has also removed their phone number from their Apple ID.
On my macs running macOS 10.14.6, the Messages app allows me to open two conversations, one for each contact, and this lets me choose whether I'm sending using SMS or iMessage.
However my iPhone 7 running iOS 15 will not let me do this! Every time I try to open a new conversation using either of the two contacts, it always takes me back to the old one, and it makes it impossible for me to choose between iMessage or SMS. Which one it allows me to send is arbitrary, and the behavior changes from day to day.
Is there any way I can fix this? It's important I be able to send this person messages using SMS when they're not at their computer.