I thinked initially yes and opened this thread too fast.
But in the end, nope, 4.19 works fine.
Tryed to get an 2,5gb/s connection with x550... But didn't readed the driver readme.
In short, i tryed to fix the linkspeed to 2,5gb/s with ethtool, but it doesn't worked xD
Even with a newer ethtool...
But finally readed the ixgbe readme and they mention there, that 2,5gb/s only works through autonegotiation and you can't set that speed with ethtool.
And well it works through autonegotiation and I can't set the linkspeed manually xD
So yes, ethtool 4.19 is perfectly fine xD
Sry for this thread.