Yes it was quite the jump from 2013 to 2021! Surprisingly, there was nothing too drastically different between 2013 and 2021 that gave it a hard learning curve.
We currently have it set to open new drawings in their own separate window instead of doing tabs. Window > Use Application Window, is unchecked. That was something we noticed about 2021 compared to 2013 was the default to have tabs.
Navigation Graphics is also set for Best Performance.