DrAzzy:
I have yet to encounter an I2C backpack where the controller wasn't wired in the "standard" way (such that the liquidcrystal_I2C library that doesn't have an option to specify the connections between PCF8574 and LCD works)
Then you either haven't played with very many devices or you have been very lucky.
There is no "standard" way to wire the PCF8574 to the LCD and that is the problem.
I have seen (and actually have) devices with 5 different pin mappings and back-light control.
While the pin mappings and active level backlight control used by the LiquidCrystal_I2C library available in the IDE library manager is popular, there are two other pin mappings and backlight control that are also quite common.
The LiquidCrystal_I2C library hard codes the pin mapping to a popular mapping.
fm's newLiquidCrystal LiquidCrystal_I2C class took the approach to support any backpack but it must be manually configured.
hd44780 took the approach to automatically figure everything out including the i2c address.
The OP was using newLiquidCrystal LiquidCrystal_I2C and had it configured to match the pin mappings used by LiquidCrystal_I2C.
But there are other backpacks that use different mappings and active level that are common.
The backpacks commonly sold under MJKDZ or GYI2LCD use the lower nibble rather than the upper nibble and use active low for the backlight rather than active high.
The backpacks sold under the name "LCM1602" that often come with 20x4 LCDs use the same pin mapping as what is hard coded in the LiquidCrystal_I2C library but use active low for backlight control rather than active high.
But there is so much copying and brand spoofing going on in these types of products that even a given name printed on the backpack doesn't mean much. I've got two backpacks that have the same name printed on them but use different pin mappings.
So you never really know what you may end up getting.
With the hd44780 hd44780_I2Cexp i/o class, it doesn't matter.
If you have a single LCD device, you plug it in and it should "just work", regardless of the i2c address, pin mapping, or backlight active level.
--- bill