Below are major improvements for JMeter 5.3 release:

Themes

Added Darklaf look and feel that improves several components.

• Light:
  • IntellJ
  • Solarized Light
  • HighContrast Light
• Dark:
  • OneDark
  • Solarized Dark
  • HighContrast Dark

Tree indentation level is easier to follow:

New look and feel themes. Light: IntellJ, Solarized Light, HighContrast Light. Dark: OneDark, Solarized Dark, HighContrast Dark.

When an element in tree is disabled, all its descendants are shown in gray. For instance, While Contoller is disabled in the following tree, so its children are gray. It is purely a UI change, and the behavior is not altered.

Note: Look and feel can now be updated without a restart

Zoom

Use CTRL + ALT + wheel for zooming fonts. Previous shortcut was CTRL + SHIFT + wheel, however, it conflicted with horizontal scrolling.In-app zoom is more consistent (e.g. sometimes not all the labels or even panels were scaled). For instance: log viewer, JSR223 code editor were not previously scaled with zoom-in/out feature.

Undo And Redo

Undo and redo support for editable fields. Keystrokes are CTRL + Z /CTRL + SHIFT + Z, or CMD + Z/CMD + SHIFT + Z depending on the operating system. Undo is implemented on a field level basis (each fields has its own history), and the history is invalidated when tree selection changes.

HTTP Samplers and Test Script Recorder

• Test HTTP/S Test Script Recorder: Name transaction controller/ simple controller using prefix without “-XXXX” suffix
• Make httpclient4.time_to_live to 60000to be closer to typical browser behavior

Improve UX

There are some UI Enhancements for the below elements.

• ForEach Controller
• If Controller
• Throughput Controller
• While Controller
• Counter Config
• XPath2 Extractor
• Function Helper Dialog
• Search popup
• JUnit Request
• JMS Elements

Precise Throughput Timer

• Precise Throughput Timer schedule generation is improved significantly (e.g. 2 seconds for 10M samples)

Function

• Bug Fix – _timeshift function does not work with offset formatters.

Report / Dashboard

• Add a ‘Median’ field to the dashboard and make the response time percentile fields support floating-point numbers.
• HTML report generation should not fail if a plugin has registered a graph and is not more present in classpath, issue a warning instead
• Response Time Percentiles Over Time, unable to change the percentiles
• View Results Tree: Allow editing of response data in testers
• View Results Tree: Keep position of split pane while switching renderer mode

References:

https://jmeter.apache.org/changes.html