How to remove someone from a group text...
How do I remove a group text person from the group I started? These instructions, https://support.apple.com/en-us/HT211302, do not work as REMOVE is not an option presented.
iPhone 11 Pro
If someone in the group text is a non-iPhone user, then there is not an option to remove anyone from the group. That is because it is not an iMessage, and you cannot remove anyone from an MMS, which is what a group text is with any non-iOS users.
From the link you provided. The bold is mine.
Anyone in a group iMessage can add or remove someone from the conversation. You can remove a person from a group iMessage that has at least three other people. But you can’t add or remove people from group MMS messages or group SMS messages.