It does not clear all private data

Shortcut tiles can be either pinned (you've added those manually so you'd need to remove these manually as well), or are the most frequent/recent sites from your history. Removing site data does not change your history itself.

Have you deleted all your history as well?

I have disabled Shortcuts. Nothing is pinned. Deleted all the history. I have attached some screenshots for reference.

The screenshot shows you have nothing shown on the home tab if that's what you call "splash screen". The only other "splash screen" being a loading animation only has Firefox brand logo and no content.

Can you elaborate a bit more where exactly you see your previous content? Thanks!

I know that’s the Home tab. I didn’t call it the splash screen. I always close Firefox from memory. As soon as I reopen it, that’s where it briefly shows the previously opened website for just a second.

Could you record a video and upload it with a bug report to github.com/mozilla-mobile/firefox-ios/issues please?

I'm suspecting what you're seeing is a stale iOS–level app screen snapshot that's shown when the app is not active (yet), so any data captured there from earlier is in the hands of the device/OS at that point.