I would like to have a numeric text entry input window pop up in a touchscreen display with a GTK window, but noticed opkg will not install matchbox-keyboard.
Could you provide the version of the hardware and software of your module? Which carrier board are you using?
Linux colibri-imx7 4.1.44-2.7.4 distro on an iMX7S 256MB v1.1B inserted in a Col Evaluation V3.2B
matchbox-keyboard is included as a Yocto recipe, which you can add to the Toradex default image. You can get a generic explanation of setting a Yocto Project environment and building our image from here.
The only thing you would need to do apart from the standard tweaking (setting the machine and maybe editing the number of parallel compilations/jobs) is to add the following line to the conf/local.conf file:
IMAGE_INSTALL_append = " matchbox-keyboard"
Please also note that the LXDE image does contain florence which may or may not fit your needs.