Hey there Bubazilla,
Thanks for reaching out to the Apple Support Communities.
To get started, when clicking on History > Show All History in the Safari menu bar, it would be expected behavior for your history to appear in your currently opened tab.
In the History dropdown menu, you would only be able to see the recent history for the previous week. For more details, check out this link here: Go back to websites you already visited in Safari on Mac - Apple Support
See websites you visited
In the Safari app
on your Mac, do any of the following:
* See websites you visited in the current window or tab: Click the Back button
or Forward button
in the toolbar (or use the Touch Bar).
* You can also click and hold the Back button or Forward button to choose a specific website. If you have a trackpad or mouse that supports gestures, swipe left or right to move through your history one website at a time. See Use trackpad and mouse gestures.
* See a longer list of recently visited websites: Click the History menu.
* See all websites in your browsing history: Choose History > Show All History.
You can also leave feedback about this feature to Apple using this next link here: Product Feedback - Apple
We hope that's able to help.
Take care!