See the schematics. This board does not negotiate PD profiles for 5A but can use more than 3A if needed and if the power supply is willing to supply without negotiation. The USB ports are fused for 1A each so USB devices alone can use 4A backed by a 5A MOSFET.
You are going to get severe ohmic losses on your past 3A on most cables and components so it is unwise to design something like the Raspberry Pi 5 where you’re using 5A. If you compare the Raspberry Pi 5’s design to Alta’s design, you will see that Pi relies on PMIC where as Alta uses discrete components. Raspberry Pi traded simplicity for fundamental design problems as seen previously on the Raspberry Pi 3 low power issues.
Using discrete components for Alta is more complex and requires more care but you get benefits like better heat dissipation, more power, better impedance matching, and faster circuit response. Alta is able to handle high power devices much better than Raspberry Pi 5 simply because it doesn’t have 5V5A going through a tiny component, much like Le Potato handles high power devices much better than Raspberry Pi 3 with the same power supply.
There are advanced PMICs that together with selective discrete components can offer the best overall design in terms of cost and performance but you’re looking at more advanced and power hungry solutions in the hundreds of dollars. For a low power and low cost SBC, use a PMIC if your power supply is 12V. Avoid it like hell if your power supply is 5V and you need > 3A like on the Raspberry Pi boards since Pi 3. It is just bad news.