If you already have a site with data in Google Search Console, there is arguably no better place to find long tail keywords than GSC. The main advantage is that Search Console surfaces queries you already appear for, which usually means they are within your realm of topical authority. That makes them far more actionable than random keyword lists from third party tools.
Start by opening the Performance report and focusing on Queries. Then use query regex filters to narrow the list down to longer searches. A simple example is (\b\w+\b\s){7,} which filters for queries that are 7 words or longer. Once filtered, comb through the list looking for terms where you are not already ranking on page 1 or 2. Those queries are often perfect content opportunities because they are tangential to what you already cover, and Google is already giving you impressions.
From there, decide whether you should create a new page, expand an existing page, or add a supporting section to match the intent.
Tools like Semrush or Ahrefs can help too, but always cross reference with real SERPs. Third party difficulty scores can be inconsistent, and Google data is generally the most trustworthy starting point.