Hi Dunwerkin2020
Welcome to the Apple Community.
Seems there a few options that may be helpful:
How to: Leave a group text message thread on your iPhone or iPad - Apple Support
says:
"You can leave a group text message as long as there are three other people on the thread and everyone is using an Apple device, like an iPhone or iPad.
If you don't see the option to leave, it might mean that one or more of the users isn't using an Apple device with iMessage".
And:
:If you can't leave a group text message, you can mute the conversation so you don't get notifications."
Discussion thread on a similar situation:
My phone doesn't show "Leave this Convers… - Apple Community
All the best :-)