I guess I have to get a separate computer just to run this software AND be able to connect it to a keyboard.

This has been rather frustrating as I'm new to Linux and there is no clear guide I could find to install Pianoteq on Linux. Can someone provide a clear and detailed guide on how to install this on my Google Pixelbook Go Chrome OS device? It is running linux as welll.

If you unzip the pianoteq download file you should find that one of the files within it is  find a file within it is README_LINUX.txt.  That file has instructions.  You could also refer instructions available in various places on how to install Pteq on a Raspberry Pi, which is a computer running Linux.  Not all of the instructions are applicable, since some are specific to setting up the Raspberry Pi itself.  However, some are, e.g., refer to section 6, "Installation of Pianoteq", in this guide:  https://www.modartt.com//downloads/gen/...Pi3_v3.pdf

I use a Google Pixelbook as my main computer, and spend a lot of time in Crostini, the Linux environment within chromeos.  However, I haven't installed Pianoteq on that machine, so can't help you there (I've installed on Raspberry Pi running Linux and on my Wiindows PC).  Crostini may be full-fledged enough by now to run Pianoteq properly, but I'm not sure.  Things like full support for audio are fairly recent (last year or so) and I'm not sure things like USB midi are fully supported yet.  They may be; I can only say I haven't checked, but that support of some USB functionality in Crostini/Linix on chromebooks may not be perfect.  If you're new to Linux and you run into problems I would say you don't want to waste too much time on it.  The Crostini Linux within chromeos differs in some ways from the native Linux environment you'd find on a regular PC running Linux. (One example of where things may differ with Crostini would be the suggestion to "set maximum CPU frequency" in Linux.  I'm pretty sure you won't be able to do this properly from the Crostini Linux environment within chromeos; it's the main chromeos environment that controls this.  This particular problem wouldn't mean you can't run Pianoteq on a chromebook, just that it may not run optimally.)