SQL Server 2019

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DECLARE @Data TABLE (Account VARCHAR(10), Item VARCHAR(100), Amount MONEY)
INSERT @Data
VALUES
	('ID1', 'Bands',        20.00),
	('ID2', 'Bands',        20.00),
	('ID4', 'Foam Roller',  40.00),
	('ID5', 'Foam Roller',  40.00),
	('ID3', 'Shirt',        30.00),
	('ID1', 'Weights',     100.00),
	('ID4', 'Weights',     100.00),
	('ID1', 'Yoga Mat',     25.00),
	('ID2', 'Yoga Mat',     25.00),
	('ID4', 'Yoga Mat',     25.00),
	('ID5', 'Yoga Mat',     25.00)

SELECT PVT.*
FROM (
	SELECT First.Account, First.Item, Second.Item AS OtherItem
	FROM @Data First
	JOIN @Data Second ON Second.Account = First.Account
) D
PIVOT (
  COUNT(Account)
  FOR OtherItem IN ([Bands], [Foam Roller], [Shirt], [Weights], [Yoga Mat])
) PVT

SELECT PVT.*
FROM (
	SELECT First.Item, Second.Item AS OtherItem, COUNT(*) AS N
	FROM @Data First
	JOIN @Data Second ON Second.Account = First.Account
    GROUP BY First.Item, Second.Item
) D
PIVOT (
  SUM(N)
  FOR OtherItem IN ([Bands], [Foam Roller], [Shirt], [Weights], [Yoga Mat])
) PVT

Item	Bands	Foam Roller	Shirt	Weights	Yoga Mat
Bands	2	0	0	1	2
Foam Roller	0	2	0	1	2
Shirt	0	0	1	0	0
Weights	1	1	0	2	2
Yoga Mat	2	2	0	2	4

Item	Bands	Foam Roller	Shirt	Weights	Yoga Mat
Bands	2	null	null	1	2
Foam Roller	null	2	null	1	2
Shirt	null	null	1	null	null
Weights	1	1	null	2	2
Yoga Mat	2	2	null	2	4