@Aleksi’s guidance is the best one as usual one if your objective is to have more space for the chart, because I believe in AppSheet chart the space below X axis line seems to be fixed irrespective of X axis label.
But just for information purpose, if I may add, if you wish to hide the title by using the display name property of the column settings for the X axis title column.
Please have an expression something like below in the [San Francisco city] column’s display name property
IF(CONTEXT(“View”)<>“Your Chart View’s Name”,“San Francisco city”, " ")
Below is an example