There could be a few reasons why a search thingy appears on startup all of a sudden. It could be that a program or browser extension is installed that is set to display a search thingy on startup. Or, it could be that your browser's settings have been changed to display a search thingy on startup.
If you're not sure why a search thingy is appearing on startup, you can try troubleshooting by disabling any recently installed programs or browser extensions. If that doesn't work, you can try resetting your browser's settings to their default values.