MW 1.35.2 runs with php 7.3.27 but mpdf v6.1.4 requires max. php 7.0.*, therefore the installation fails
# composer install --no-dev
Loading composer repositories with package information
Installing dependencies from lock file
Your requirements could not be resolved to an installable set of packages.
Problem 1
- mpdf/mpdf v6.1.4 requires php ^5.4.0 || 7.0.* -> your PHP version (7.3.27) does not satisfy that requirement.