What exactly needs to be different for your open source projects than for the others - email address?

Is fixed in build 14215.

There were several reasons why we didn't made the "fixup!" prefix the default. One is that when selecting a message from a previous commit it would have required an option (existed before). Instead of the limited Git default way, we thought for a GUI our 3 options in the Interactive Rebase dialog are more suitable and cover more use-cases.

What is your exact suggestion?

What commands you miss most?

Please request this by the developers of your used Linux/GTK-theme.

This also should work if the commits have the same message.

This looks like Linux. What desktop you are using? Is it configured to use 200% scaling? You already can set the low-level property smartgit.gui.dpiFactor to 1 or 2 (100% vs. 200%) in smartgit.properties.