I just updated my ‘Count Characters for Micro.blog Timeline’ shortcut to version 1.1:

• Added an option to continue with post containing too many characters to be displayed in full on the timeline. Feel free to publish posts as long as you want! Just note that it will be truncated on the timeline.
• Included the character limit in some prompts as a reminder of what to aim for. (Example: 787/600)
• Changed the icon to use the calculator glyph.

Get it here from the HeyDingus Shortcuts Library.

Thanks @pratik!