CircuitMaker warning: How to define ports?
The warning tells you pretty straight-forward what the issue is: An I/O-pin is connected to an Output Port. It's one of those warnings that in many cases could be disabled, since it might contribute more clutter than it provides useful information.

More specifically, the issue is that the pin on your schematic symbol is an Input/Output-pin, which Altium considers to be both input and output, instead of one of them. When you then connect this to an Output Port (arrow pointing away from connection), it warns you that there might be an issue.

The annoying part of this is that many standard / manufacturer-created symbols use IO-pins to indicate user configurable pins on MCUs.

To get rid of the warning, either edit your symbol to be either an input, output or non-directional pin, use a generic Port, or put a No ERC-marker on the connection.

Also, you should ensure that only the driving source has an Output Port-object, and the receivers have an Input Port-object. It doesn't really matter electrically, but it provides clarity when reading the schematic.