here's another version but for selected text, specifically. https://routinehub.co/shortcut/12439
Requirements (sortof)
This shortcut is a modification of my Make Audio of Article Body Siri Speech Synthesis shortcut designed for convenient use from the share sheet. Considering how often I have personally come across text on (on iOS and iPadOS, especially) which I'd like to hear read aloud that does not have a corresponding parseable article on the web (Apple News articles, Apple Notes, release notes, Testflight release notes, etc,) I thought this use warranted a shared shortcut of its own.
Upon installation, you will be required to specify a system or iCloud Drive folder in which the encoded synthesized audio files will be saved. At run, you will be asked to provide a title via an Ask for Input action. This shortcut requires the Actions app (which is completely free and universal across Apple platforms,) in order to eliminate any spaces in said title for the ideal filename. Those who'd prefer not to use said app for whatever reason might delete its action and set the Save File action to Ask Where to Save to specify a filename for each run.