If you never touched RouterBOOT settings, the same way booted OpenWRT initramfs.
Read the manual here to understand the LED patterns: https://help.mikrotik.com/docs/display/UM/LHG+R#heading-Resetbutton
At boot, you hold in the reset button until the LED goes out (~25 seconds). For netinstall you can keep holding it in until device shows in netinstall software, no difference.
You can watch the port you are using with tcpdump or wireshark. Need to see BOOTP
If you had changed boot proto to DHCP, you will need to reset RouterBOOT settings (hold reset button 5-10 seconds at boot. see reset RouterOS configuration to defaults in manual page.)
Netinstall on linux only uses the first interface. I used macvlans to get around this.
There is a difference between starting to hold the reset button before power on (backup bootloader), or after power. Try both if not working.