See https://web.archive.org/web/20221027220343/http://lsauer.net/chrome-session-restore/#.
While you're on that page, click the badge at the left of the address field (usually a lock icon), goto "site settings" and set pop-ups and redirects to "allow".
Then, right-click on the max tabs field and choose "inspect element". Then, in the developer tools, right-click on "max=", choose "edit attribute", delete all of it and press ctrl + enter. Then, edit the value attribute and set it to 1000 and press ctrl + enter to apply your change.
Then, on the page, click "choose" and point it to the session file you want to load. There will then be a menu you can click on to see all the tabs. There will even be an option to open all of them in tabs (which is why you need to allow popups).
Session_xxx files are for open tabs and Tab_xxx files are for recently-closed tabs.