Update 3.5.15.1 - Fixed a bug where the Updates utility wasn’t showing “Update” buttons The update button is missing, and the fix is available, but impossible to initiate from the CP.

Before I embark on a manual update, I wondered if there was a URL that I could use to trigger the update? (What URL does the button normally run?|)
Cheers
Matt
Not a URL, but you can do it from the command line by running either:
php craft update craft

Or
composer update craftcms/cms

You can see the issue for this here: https://github.com/craftcms/cms/issues/7091