I can’t get shortcut app on mac to notify low battery

mobin ~ Unlike iOS & iPadOS, macOS Sonoma does not provide for 'automation' in Shortcuts app — so shortcuts have to be run manually. However, this third-party app:

Shortery
 – Automation for Shortcuts

...includes a Time trigger: "Set a time when the Shortcut should run and define how often it should be repeated."

By the way, your shortcut's Repeat action is redundant — as there will only be one item returned from the previous Get Battery Level action.

Shortcuts User Guide for Mac - Apple Support

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Shortcuts unfortunately tends to be struggle with many things, yes.

Maybe an existing example (one not using Shortcuts) can help?

• https://stackoverflow.com/questions/53997451/script-to-play-a-warning-when-battery-level-is-under-a-threshold-in-macos

If the Mac is Apple silicon:

• https://github.com/actuallymentor/battery
• https://github.com/zioninzion/M1MacBatteryLimiter

Customizing zsh prompt (and another shell example):

• https://derrick.blog/2023/07/19/macbook-battery-stats-in-your-zsh-terminal-prompt/

As for commercial alternatives, some folks are fond of the iStat Menus app.