Tracking “Nala – APT on Steroids” article should help there, should help you. Also, please let us know if this guide helped you to install (easy one) and in particular how the nala package works for you. Thanks for the linked info/video (although didn’t watch it, not yet)! Actually linked article self-defines that this package doesn’t come from Debian 11 repo (therefore …).
I took an educated guess and opted for the nala_legacy package, and that seems to have been the correct choice. It’s working, although I do get the odd flatpack error here and there.