How to load a cookie banner through Google Tag Manager

Google Tag Manager

Step-by-step: paste your privacy policy URL

Generate your hosted cookie banner script URL.
In GTM, create a Custom HTML tag (or a tag that injects the script src) that loads the banner.
Trigger the tag on All Pages, with consent initialization ordered before marketing tags.
Publish a GTM workspace version and verify on a staging page that the banner appears once.
Confirm Analytics/Ads tags respect the consent state after interaction.

Can I put the banner only on landing pages?

You can, but consent should cover every page where tags fire. Sitewide install is safer.