changelog: pppoe-server has auto mtu feature (enabled by default for new pppoe servers)

Where is that feature? When I can enable/disable/set that feature? (Auto MTU for PPPoE server)

Console only - mtu=auto

I already tested the v6.20 unfortunately we can't find any new feature for pppoe-server nor bridge. but with console i can found auto with MTU. hope they can fix that for next update
regards

It is all there. If you need winbox support - download latest 6.21 RC version from download page