PWM fans are not recognized as PWM and cannot be controlled using a curve (smart-profile) from (the most recent) Fan XPERT 4,
when those fans are connected to the EXT* 4-pin fan ports on the ASUS Fan Extension Card.

The extension card is connected to the ROG z270 Formula IX motherboard using the 5-pin control cable from the EXT_FAN header on the mo-bo.
It is powered by the 12v molex connector. The extension card page lists the motherboard as supported.

The fans are industrial Noctua F14 3000 rpm fans.
I can control correctly those fans from the BIOS in almost their full profile range 5%-84% (150 - 2500 rpm) when connected to the EXT* headers in PWM mode.
When connected to the EXT* headers they are recognized as DC (only) in Fan XPERT 4 and can only be controlled using a fixed RPM setting.
Alternatively, they can be switched in BIOS to DC, which allows to control those fans from Fan XPERT 4 in DC mode.
Switching to DC results in an odd control curve being recognized with starting point at 1300 rpm - which is not very soft on ears.

When connected to the HAMP header or the CHASIS fan headers, the fans work properly with BIOS and Fan XPERT 4 as well in PWM mode.
Also, I have tested Fan XPERT 4 and the extension-card headers using "Be Quiet" 1000 rpm fans - with the similar results.

I assume this is a missing support from Fan XPERT 4 on my motherboard model.
I have seen similar issues with Fan XPERT 3 software reported for ASUS motherboards.
Unfortunately, I cannot test with another ASUS Fan Extension Card because they are nowhere to become.

My OS is Win10 64 bit.