NuttX configuration
NuttX offers a wide range of configuration options and features that can be enabled with one of the available Kconfig frontends.

Install Kconfig frontends

NuttX uses a similar configuration system as the Linux kernel. There are Kconfig files that define the different options and you can generate a configuration file that can be used by the build system with a Kconfig frontend.
NuttX provide their own fork/back-up of the Kconfig-frontends, to make sure that they always have access to a compatible version. It is still hosted on their old BitBucket repository.
In Ubuntu 20.04 it is possible to directly install the kconfig-frontends package from the package repositories. You only need to run apt install kconfig-frontends.
You can then skip most of the instructions below.
First, make sure you have gperf installed:
sudo apt install gperf
Then download the source code by cloning the NuttX Tools repository from BitBucket:
git clone https://bitbucket.org/nuttx/tools.git
Change the working directory to the kconfig-frontends folder:
cd tools/kconfig-frontends
Configure the build to include (at least) the menuconfig and qconfig tools. The Kconfig frontends will be installed into the /usr folder.
./configure --enable-mconf --enable-qconf --prefix=/usr
Now build the tools according to the configuration that we just created:
make
And finally install the Kconfig-frontends that we just build from source:
sudo make install
Once you have a "default" configuration in place (we will get to that in a second), you can edit the configuration with make menuconfig or make qconfig. Both tools have their pros and cons, just give them a try and see which one you like the most!

Start with a canned configuration

Make sure you are inside the "nuttx" folder:
cd ~/src/apache-nuttx/nuttx
Then use the configure script to select the "nshdebug" configuration for the "rddrone-uavcan146" board:
./tools/configure.sh rddrone-uavcan146:nshdebug
Make sure to first run make distclean if you still have another active configuration.

Configuration

Menuconfig is the "default" tool to configure the NuttX build. Once you have a board configuration selected (see above) you can edit the configuration with:
make menuconfig
You can also use qconfig, which shows the configuration as a nested list instead of different menus. This might make it a bit easier to navigate through the many options that are available:
make qconfig
Menuconfig and qconfig are easy to use tools, but NuttX is very configurable and you can easily got lost in the hundreds of menus and options that it provides. Take your time to explore the options that NuttX has to offer, but don't try to enable many options at once. Just select a few, build the code and give it a try on the hardware itself.