HTACCESS / Redirect all pages from Alias-Domain to Main-Domain except one Pathsegment

Question

i have an alias domain "example.tld" and i want to redirect all pages to the main "domain example.de" except of one path.

because we need "example.tld" only for landingpages.

For example:

example.de -> example.tld
example.de/somepage -> example.tld/somepage
example.de/landingpages -> should not be available
example.tld/landingpages/.. -> example.tld/landingpages/..

Is this possible?

Thank you!