In the old days, it used to be a problem because everyone just connect their windows 98 desktop with all their services directly exposed to the internet because they’re using dial up internet without the concept of a gateway that prevents internet from accessing internal resources. Now days, you’re most likely behind your ISP router that doesn’t forward ports by default, and you’re only exposing the things you’d actually want to expose.

For things you’d actually want to expose, having a service on the default port is fine, and reduces the chances of other systems interacting with it failing because they’d expect it on the default port. Moving them to a different port is just security through obscurity, and honestly doesn’t add too much value. You can port scan the entire public IPv4 space fairly quickly fairly cheaply. In fact, it is most likely that it’s already been mapped:

https://www.shodan.io/host/

Keeping the service up-to-date regularly and applying best practices around it would be much more important and beneficial. For SSH, make sure you’re using key based authentication, and have password based authentication disabled; add fail2ban to automatically ban those trying to brute force. For Minecraft, online mode and white listed only unless you’re running a public one for everyone.