It used to be, on some mail readers, that "opening" an email message could unleash Pandora's Box, in terms of interpreting HTML, downloading images, attachments or whatever. I sincerely doubt that is even the case for the major providers such as Outlook or Gmail. And yeah, per comments downthread, my Android Messages app has "read/unread" and that's really the only thing that "opening a text" changes. There's no additional execution or activation like opening or executing a file.

How does one “open a text”?

I agree. It's also worth noting that people have had their devices compromised just by opening a text message (for that matter iphones have been hacked just by receiving an invisible text) so it's probably best to delete any spam text unread.