i cant make a export.

Try first a reset of Lightroom's preferences to the default settings:  How to reset Lightroom Classic preferences (adobe.com)

It's recommended to backup your preferences before you reset the preferences:

https://helpx.adobe.com/lightroom-classic/kb/preference-file-and-other-file-locations.html

If this doesn't help try to switch off the GPU support from the Lightroom preferences, because GPU is also used for export. and check if that helps to fix the issue. 

Go to Lightroom > Preferences > Performance tab > Uncheck "Use Graphics Processor" > Restart Lightroom.

https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-gpu.html

If it's help see here Troubleshoot GPU issues | Lightroom Classic (adobe.com) and check the different steps.

If this also doesn't help check if your system is up-to-date. Do you have installed all recent updates and patches for the operating system and the device drivers, especially the graphic driver? If you have a NVidia graphic card installed, make sure that you are using the recent Studio version of the driver, not the Game Ready version.

Please provide a copy of your 'System Info'. This can be get from the LrC Help > System Info menu item. There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.

What app are you using? What version NUMBER?

What operating system? What version NUMBER?