xcode-build-for-simulator step doesn't support watchOS in its inputs . The workaround is to use a script step like below
- script@1:
inputs:
- content: |-
set -e
WATCH_SIM_ID=$(xctrace list devices | grep -m 1 "Apple Watch Ultra (49mm)" | awk '{print substr($0,length($0)-36,36)}')
xcodebuild -project $BITRISE_PROJECT_PATH -scheme $BITRISE_SCHEME -destination "platform=watchOS simulator,id=$WATCH_SIM_ID"