-The first thing I did when I looked at the screen shot was to look at the CONSOLES alert.

-The CONSOLE alert looked like it was referencing a script called Card in the player input script.
(Scripts do work with other scripts; that's how we make such interesting games).

-I opened a finished working version of the Prototype that was made in Unity 2018.
(It is available at this link if you need to reference it: 

http://berkeleycollege.professorklein.com/Fall_2021/Follow_Along/01_Memory/2018_as_we_go/fin/Sample.zip

-If you look in the folders with the video lessons, I put full project files in certain folders that represent
starting/stopping points towards completion. Those were project files were created, however, in Unity 2020).

-I removed the Card script from my Scripts folder; the project called the same console error:

http://berkeleycollege.professorklein.com/Fall_2021/Follow_Along/00_OnRequest/Alyssa/DmXriHx5id.png

-I put the script back and the error was gone, because the reference was now fullfilled:

http://berkeleycollege.professorklein.com/Fall_2021/Follow_Along/00_OnRequest/Alyssa/Unity_cpyvUXx0BE.png

-Perhaps you are referencing code from a future installment of our little videos?  Perhaps you are referencing the Card.cs file before you have created that very file? 
I suggest you look at your PlayerInput code closely and remove the line 
that is referencing it for now, since you are simply trying to move on with your coding.

-Notice how I zip the entire project file in various instances? It is a good idea once you make progress.
Follow this process for yourself, or you can send me the project file. I would be more than
happy to help get it back on the road so that you can complete the entire project.

-Exporting the game happens at the end. We are working within the game engine so we need the full
project files in order to prepare our Prototypes for building. No game can be exported that is calling
console errors in red. Yellow ones are more like warnings and the game will build with them.