Sure you can. It is your system - you can do what ever you want.
→ Install Podman Desktop on Linux | Flathub
→ Podman - ArchWiki
→ Linux Containers - ArchWiki
Understanding the package manager and how this works will be incredibly helpful in deciding how you customise your system.
→ Arch package guidelines - ArchWiki
→ Arch User Repository - ArchWiki
→ AUR submission guidelines - ArchWiki
Using python venv and nvm/pnpm the applications are effectively run in separate environments in your user’s home folder.
AUR does not work like that but using AUR you are effectively building a package that will be added to the system and tracked by pacman.
If that is not what you want - you can use flatpak, snap or even containerise using docker or podman.
When it comes to apps based on nodejs - unless you want pacman to track the files - you simply download the archive from the vendors website - unpack it into a convenient folder inside your home - then run the app.
The [Postman application] is a good example, but you could as easily use the same method for the WhatsApp client.
You can also place the app in the /usr/local tree with a launcher in /usr/local/bin.