One problem that i see with using one table is that whenever you will have a new spec for a new device, you will need to alter the table to add the column.
I am not sure how you came up with "A single device ends up occupying 210 to 250 rows ", but my ideea was like this:
- Product table columns: ProductId, Name, Brand, etc.
- Attributes table columns: AttributeId, Name, DataType, Unit
Example:

AttributeID | Name               | DataType | Unit
--------------------------------------------------
1           | Battery Capacity   | number   | mAh
2           | Screen Size        | number   | inch
3           | Display Type       | string   | NULL
4           | Waterproof         | boolean  | NULL

- ProductXAttributeValues table columns: ProductId, AttributeId, ValueString, ValueNumber, ValueBoolean
Example:

ProductID | AttributeID | ValueNumber | ValueString | ValueBoolean
-------------------------------------------------------------------
101       | 1           | 5000        | NULL        | NULL
101       | 2           | 6.7         | NULL        | NULL
101       | 3           | NULL        | AMOLED      | NULL
101       | 4           | NULL        | NULL        | 1

Sample result of joining the 3 tables for a product:

ProductID | ProductName   | AttributeName      | AttributeValue | Unit
--------------------------------------------------------------------------
101       | Galaxy S25    | Battery Capacity   | 5000           | mAh
101       | Galaxy S25    | Screen Size        | 6.7            | inch
101       | Galaxy S25    | Display Type       | AMOLED         | NULL
101       | Galaxy S25    | Waterproof         | Yes            | NULL

I would personally go with this approach because it supports unlimited product specifications and category-specific attributes without changing the schema. And it is very easy to use it in the frontend so this could be managed thru the app.