If you are having issues with selectboxes on front or back-end it is usually an issue with bootstrap.
In the main wpDataTables settings you can find the options to include full bootstrap front and back-end which are automatically turned on. Try turning off the option Include full bootstrap front-end and let me know if the issue is resolved.
Check under catagories and GEO tab of this url. Your multiselectbox isn't working. The only reason i puchased your premium version for is not working
https://crective.com/product-category/german-guest-post/
Hi Affan
Thank you for reaching out to us.
If you are having issues with selectboxes on front or back-end it is usually an issue with bootstrap.
In the main wpDataTables settings you can find the options to include full bootstrap front and back-end which are automatically turned on. Try turning off the option Include full bootstrap front-end and let me know if the issue is resolved.
Do let me know if this helps.