Mastodon requires a load balancer or reverse proxy to properly terminate TLS/SSL connections between users and ingress traffic to the system.
Nginx is commonly used for this purpose, and an example configuration is provided in the Mastodon repository.
There are no specific version requirements for Nginx, and other types of software can be used in place of Nginx, such as Caddy for example.
Regardless of the ingress software that is used, you should keep it up to date to prevent exploitation of known security vulnerabilities.