I just discovered that my mactelnet (debian mactelnet-client 0.4.4-4 package) can’t login anymore with routeros 6.45.3, and probably with any version later than 6.43
mactelnet is not a MikroTik product!
It was made by an independent developer after reverse-engineering (and maybe some hints here) of the protocol.
Now the protocol has changed and a MikroTik employee has stated there is no documentation available yet. Maybe in the future.
So you either have to hope that someone is interested in going through the trouble of reverse-engineering it or either wait for that documentation first and then hope someone implements the changes.