DisplayPort over USB-C resolutions

DisplayPort over USB-C often does not have the required bandwidth for more than two 1080p screens. This mainly depends on two factors: DisplayPort version and link configuration (number of DisplayPort lanes).

High Bit Rate 2 DisplayPort (specified in DisplayPort 1.2, what you have) supports up to 5.4 GBit/s per lane.

USB-C DisplayPort Alt Mode features 1, 2 or 4 DisplayPort lanes (but no USB SuperSpeed at 4, only High Speed).

One 2560x1440@60Hz screen requires 5.63 GBit/s, meaning it requires two DisplayPort 1.2 lanes (but only 1 at DP 1.4). Adding a 1080p screen would require another lane, requiring the maximum amount of 4 lanes in the USB-C link.

Your 1080p screen indicates in its specs that it features "USB Type-C (Alternate mode with DisplayPort 1.4, USB 3.1 upstream port, Power Delivery PD up to 65 W)". The description strongly hints at it only using 2 DisplayPort lanes. This is enough for at least two screens of this type. DisplayPort 1.4 doubles the available bandwidth, allowing for more and larger displays.

There is of course a workaround: Thunderbolt. Because it uses a different type of link, it can support (at least) two 2560x1440@60Hz screens over a single cable. The drawback is of course that Thunderbolt docks are very expensive.