Apple changed the way Safari looks in iOS 15 by moving the address bar at the bottom. Not everyone likes it and you can restore the old behavior if desired.
To restore the old version, click on the two AA on the left side of the address bar and select the first entry “Show Top Address Bar”.
To use the new version again, do the same but now click on the last entry called “ Show Bottom Tab Bar”.
As an alternative, you can also adjust this setting in the Settings app in Safari > Tabs.