Log4j is a Java library by Apache used to log debug messages within applications. Laravel Forge https://forge.laravel.com does not install Log4j by default. Furthermore, Forge does not install any applications known to use Log4j. The vast majority of servers provisioned by Forge will not be vulnerable; however, if you have manually installed applications such as ElasticSearch your server may be affected.
However, if you have manually installed libraries, use custom layers, or customize your Dockerfile, it is possible that Log4j has been installed due to those modifications.