Can the 2021 Land Rover Defender make a U-turn?

Yes. Fits a 40 ft street.

37ft curb to curb

Street width, feet

Street 40 feet curb to curb.

2021 Land Rover Defender 90 AWD. Top view, to scale.

2021 Land Rover Defender: turning circle by trim, 40 ft street
Trim	Circle, ft	Margin	One move
90 AWD	37	+3 ft	Yes
90 S AWD	37	+3 ft	Yes
110 AWD	42.1	-2.1 ft	No
110 Standard AWD	42.1	-2.1 ft	No
110 S AWD	42.1	-2.1 ft	No
90 X-Dynamic S AWD	37	+3 ft	Yes
110 SE AWD	42.1	-2.1 ft	No
90 First Edition AWD	37	+3 ft	Yes
110 X-Dynamic SE AWD	42.1	-2.1 ft	No
110 X-Dynamic HSE AWD	42.1	-2.1 ft	No
90 X AWD	37	+3 ft	Yes
110 X AWD	42.1	-2.1 ft	No
90 Standard AWD	42.1	-2.1 ft	No

What this cannot tell you

Curb-to-curb turning circle as listed.

Mirrors and overhang need more room.