Power Armor
Artifact
Domain — 
: Target creature gets +1/+1 until end of turn for each basic land type among lands you control.
"Great peril demands formidable weaponry." —Urza
Doug Chaffee
The List (PLST)
• #INV-309Rulings
The basic land types are Plains, Island, Swamp, Mountain, and Forest. Land types other than basic land types (such as Desert) don't contribute to domain abilities.
(wotc • 2021-06-18)
Domain abilities count the number of basic land types among lands you control, not how many lands you control or how many of any type.
(wotc • 2021-06-18)
Rulings
The basic land types are Plains, Island, Swamp, Mountain, and Forest. Land types other than basic land types (such as Desert) don't contribute to domain abilities.
(wotc • 2021-06-18)
Domain abilities count the number of basic land types among lands you control, not how many lands you control or how many of any type.
(wotc • 2021-06-18)