When there are multiple plots (no matter data plot or function plot), Origin uses the 1st plot’s long name, unit as axis title. See the Data Plot Index for Auto Axis Titles dropdown list on Legends/Titles tab of graph node of Plot Details dialog.

So if the function plot is the 1st plot in graph window, F1 will show as axis title. In Origin 2023, we will skip using function plot as axis title unless it’s the only plot in the graph.

Use system variable @FPT=1 to roll back to the old behavior.