I have an x86 PC running OpenWRT 24.10.0 that has 3 ethernet ports in the br-lan bridge interface, is there a way to set these ports to act as a switch? I'd like it if the connected devices could communicate directly with each other.
If the ports are already in the br-lan bridge, they will indeed behave like a switch. However, unless this device is serving a more processor intensive purpose on your network (i.e. as a router), I agree with @anomeome that you should just use a purpose built switch -- much lower power (thus cheaper to operate and better for the environment), smaller, very inexpensive.