Basically a simple server listening on a port will experience hundreds of random script-probing attacks per day. And if any of them show the slightest hint of succeeding then that escalates quickly to thousands per minute.
You don't need a DNS entry to "expose" the IP address (there are only 4 billion). Moving to another port reduces, but doesn't eliminate the traffic.
Telling people this freaks them out. But as long as the server is done well its just noise.
There are groups out there just looking at the certificate transparency logs to get the newly added certs to scan.
Back then, I mostly only ran Linux, but for some reason, I needed to run something on a Windows machine, so started installing Windows 98 SE onto a machine, and set it up with a public IP address without even thinking about it. It crashed before it'd even finished installing [0], and investigation showed that it'd been whacked by an automated RCE exploit scanner.
I immediately decided it was never worth the risk of putting a Windows machine on a public IP, and set up a NAT even though I had 3 spare public IPs.
[0] There was already a published update to protect against this exploit, but I was scanned and hacked between the base install exposing the bug and the automatic update patching it.
The internet is a wild place in any aspect of it. You should try spinning up a random virtual private server on any cloud provider, plug in a public IP address,and listen to traffic. Sometimes it takes seconds to get your first traffic from vulnerability scanners.