You must use single quote strings when making a SOQL query to Salesforce.

Salesforce supports only single quote strings in a SOQL query. Therefore, the following inputs would not be recognized by Salesforce.

let inputs = { "productsArray": '("Tablet10", "Laptop13", "Laptop15")' }

Instead, use single quotes as in the following snippet.

let inputs = { "productsArray": "('Tablet10', 'Laptop13', 'Laptop15')" }

The following sample script pulls Salesforce IDs.

// Array of Salesforce IDs
const idList = ['0066e00001pGlTUAA0', '0066e00001pGlTTAA0', '0066e00001pGlTPAA0'];

// Create a string to pass to the SOQL IN query
// first part: "('" = opening parenthesis and single quote
// middle part: idList.join("','") = join all the Salesforce Ids with single quote, a comma and single quote
// last part: "')" = single quote and closing parenthesis
const soqlIn = "('" + idList.join("','") + "')";

// inputs to the SOQL query and calling SF connection
const inputs = {"idList": soqlIn};
const response = Salesforce.<yourExternalConnectionVariableName>(inputs);