Despite being split, 7-Zip recognizes the set as one entity. You only need to interact with the first file ( .001 ) to extract everything. How to Extract .7z.021 Files
Place all 21 parts ( .001 - .021 ) into the same directory. Open the First Part: Right-click the .001 file. 5EK18EZQ6L.7z.021
Select 7-Zip > Extract Here or Extract to "folder" . Despite being split, 7-Zip recognizes the set as one entity