Exclude from Cache

Looks like there was a Drupal 7 version so it might be straightforward to port to Backdrop .

Edit: yup, it is a really small module, and easy to port. https://git.drupalcode.org/project/cacheexclude/-/tree/7.x-2.x?ref_type=heads. Give it a try!

Depending on the exact use case, there is another interesting module which is already available for Backdrop: Entity Cache Administration

Entity Cache Administration provides an interface that lets the site administrator select which entities should be cached at the individual bundle level. For example, you can choose to cache some content (node) types but not others.