Gigabit speed disconnects macmini late 2012

There are various posts on this subject , but cannot find if there is a software solution..

Briefly, Broadcom model 57766-A1 ver 10.3.5.

If you run on Auto it defaults to 100 and works OK. If you manually change to 1000 it will disconnect.

It would appear to be driver related - using catalina , although probably been like this for years.

Apple support, trying to be helpful cannot find solution.

This is also related to Incompatible Kernel Extension Configuration Data: but not sure what version is

relevant to ethernet ?

Rather than waste hours searching the forums, will buy Thunderbolt to Gigabit Ethernet Adapter.

Have posted to bring this subject to the top and in case someone has same problem albeit

on relatively old mac models.