For the Editor Area
VS Code started changing the default value of the editor.stickyScroll.enabled setting to true in VS Code 1.86 (see the iteration plan and issue ticket #202655).
There are multiple ways to turn it back off:
Right click the sticky scroll panel to be prompted to toggle it off
OR Run View: Toggle Sticky Scroll in the command palette (corresponding command ID is editor.action.toggleStickyScroll)
OR Open your user settings.json file by running Preferences: Open User Settings (JSON) in the command palette, and write "editor.stickyScroll.enabled": false and then save the change
Sticky Scroll was released in version 1.70 (July 2022), but up until version 1.86, it had been disabled by default.
The default has now been fully changed to on in version 1.87. You can also change the maximum number of lines that the sticky scroll panel takes up with the editor.stickyScroll.maxLineCount setting.
Note that sticky scroll is also supported in several other areas of the VS Code workbench, such as the terminal and tree views, which each have their corresponding settings and commands.
If you want to adjust the colour, open settings.json, create a key for workbench.colorCustomizations, and then trigger suggestions and type "stickyscroll" and you'll see what options there are.
For the Terminal
The default for sticky scroll in the terminal is (probably) changing in VS Code 1.89 to be enabled by default (issue ticket #209003). You can disable it using the terminal.integrated.stickyScroll.enabled setting, or toggle it using the Terminal: Toggle Sticky Scroll command (corresponding command ID is workbench.action.terminal.toggleStickyScroll).