Hello @cromsan,
If the Marketplace tab appears greyed out like in your image, it is likely that your Online Functionality setting is currently disabled. This can sometimes happen if the sim loses connection to the servers. You can re-enable this setting (which should restore the Marketplace for you) by following the instructions mentioned by several forum posters above:
Browse to this setting and make sure it is set to ON: Options -> General Options -> Data -> Online Functionality
Please give this a try and let me know if that fixed your issue.
Thanks,
MSFS Team