Raspberry 4B - Dualband 2.4GHZ and 5GHZ

Question

I am aware that the question is asked here already, e.g.

1. Can RPi4 run simultaneously on dual band (WiFi 2.4GHz / 5GHz)?
2. Is it possible to use Raspberry Pi 3 B+ Dual Band WiFi Simultaneously?

But I have several problems with it. The sudo iw list lists:

--- snip ---
valid interface combinations:
     * #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
       total <= 3, #channels <= 2
     * #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
       total <= 4, #channels <= 1
--- snip ---

Than I can use either a P2P-deviceor a AP device. But honestly I have no clue what is the main difference between them. Does it mean I cannot use any longer RaspAP?

Beside the theoretical issue I have no clue how to set up the Raspberry serving on these different bands. The instructions of link1 failed. Issuing a sudo wpa_cli I get

wpa_cli v2.8-devel
Copyright (c) 2004-2019, Jouni Malinen <j@w1.fi> and contributors
This software may be distributed under the terms of the BSD license.
See README for more details.
Selected interface 'p2p-dev-wlan0'
Interactive mode
<3>CTRL-EVENT-SCAN-RESULTS
<3>CTRL-EVENT-SCAN-RESULTS
<3>CTRL-EVENT-SCAN-RESULTS
> p2p_group_add freq=5
FAIL
<5>P2P: Failed to add group interface

Any ideas how to continue with a proper config?

Answer 1

I reference my answer to the question you have quoted as first link:

1. Can RPi4 run simultaneously on dual band (WiFi 2.4GHz / 5GHz)?

You wrote:

Any ideas how to continue with a proper config?

You don't tell us what this proper config should be. If you mean to have a dual band access point, then I quote the second sentence behind the link:
If one interface is used as access point (AP) you can only use one band.
If you need dual band then you have to use an additional USB/WiFi dongle.

Than I can use either a P2P-device or a AP device.

This is not right. You have two combinations. The first is:

 * #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
   total <= 3, #channels <= 2

and the second combination is:

 * #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
   total <= 4, #channels <= 1

With this one you can have ONE #{ P2P-device } together with ONE #{ AP } but you can only use #channels <= 1.

For example it is not possible to have a P2P-GO (group owner) together with an AP. There is no combination for it available.

Than I can use either a P2P-device or a AP device. But honestly I have no clue what is the main difference between them.

There are some different WiFi connections possible. The most used one is a well known access point to which managed clients (stations) can connect. Then you often find Wi-Fi direct that is mostly used by smartphones to connect direct for example to printer (or other devices). Wi-Fi Direct is completely different from an access point and managed with the P2P-device, P2P-client and P2P-GO. An example you can find at Setting up Wifi direct (wifi p2p) and DHCP server.

Does it mean I cannot use any longer RaspAP?

RaspAP has nothing to do with this discussion about configuring WiFi interfaces. I haven't used it but as far as I know it is a script that configure the interfaces for its use case and encapsulated it to the user so he doesn't have the burden to do it. If you want to have a different setup, you have to modify RaspAP.

The instructions of link1 failed.

I have just updated and tested the proof of concept (it isn't more) behind the link and can confirm that it works as described. Please check, what you have made different. Start with a fresh flashed image.