Doc  says:
From late experiences (with 6.48.4), it seems you cannot force a link to settle on a 2.5G or 5G rate.auto-negotiation (yes | no; Default: yes) When enabled, the interface "advertises" its maximum capabilities to achieve the best connection possible.
Note1: Auto-negotiation should not be disabled on one end only, otherwise Ethernet Interfaces may not work properly.
Note2: Gigabit Ethernet and NBASE-T Ethernet links cannot work with auto-negotiation disabled.
Having this capability, even only between two MT devices would be nice thing to have given overheating issues with 10G/s on copper.
 https://wiki.mikrotik.com/wiki/Manual:I ... e/Ethernet