I've tested that feature on your site. Adding Catalog New Product List works fine, but Catalog Product List has the error.
I Can see that you have installed at least 3 3rd-party modules: Mageplaza SMTP, Product Inquiry, and Amage Cms (Import/Export CMS). So, let's try to disable all of these modules to check if Catalog Product List Wiget works or not.
Run the following commands to disable 3 3rd-party modules:
bin/magento module:disable Mageplaza_Smtp Sparsh_ProductInquiry Amage_Cms
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
Then go to the frontend to test the result.
Case 1: If after disabling 3 modules above the issue still persists, enable these modules again and continue debugging.
Run the following commands to enable 3 3rd-party modules:
bin/magento module:disable Mageplaza_Smtp Sparsh_ProductInquiry Amage_Cms
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
Case 2: If after disabling 3 modules above the issue is resolved, enable each module one by one to test.
2.1: Run the following commands to enable Mageplaza_Smtp module:
bin/magento module:enable Mageplaza_Smtp
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
Then test
2.2: If after enabling Mageplaza_Smtp module the issue is still resolved, that means Mageplaza_Smtp module does not cause the error. Run the following commands to enable Sparsh_ProductInquiry modules:
bin/magento module:enable Sparsh_ProductInquiry
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
Then test
2.3: If after enabling Sparsh_ProductInquiry module the issue is still resolved, that means Sparsh_ProductInquiry module does not cause the error. Looks like Amage_Cms module causes the error, but still need to check for sure. Run the following commands to enable Amage_Cms modules:
bin/magento module:enable Amage_Cms
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
Then test, if after enabling Amage_Cms module the issue persists. Run the following commands to disable that module:
bin/magento module:disable Amage_Cms
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f