How to remove yourself from a group text, iPhone 8

You can only remove yourself from a group text if everyone in the group is using iMessages (blue). If anyone is using SMS (green) messages, you can't remove yourself. You will need to mute the group or block the participants.

Add or remove someone from a group conversation

Anyone in a group iMessage can add or remove someone including yourself from the conversation. You can remove a person or yourself from a group iMessage that has at least three other people. You can’t add or remove people or yourself from group MMS messages or group SMS messages.

Types of group messages

The three types of group messages that you might see are: group iMessage, group MMS, and group SMS. The Messages app automatically chooses the type of group message to send based on you and your recipients' settings, network connection, and carrier plan. For example:

• If you and your recipients are using Apple devices and iMessage is turned on, then the group message is sent as an iMessage.
• If you send a group message to people who aren't using iMessage, then the message is sent as an MMS or SMS message.

If --> Can't mute group messages - Messages Help - Google Support