Honestly this smells more like a code bug than a build error.
Judging just from stack trace noise, perhaps one of your Linq statements is blowing up, who knows for what reason. Looks like it might be catching and re-throwing an exception? It looks like perhaps some lambda-making mechanism failed, but not really sure. I would start there, see if you can track down which one it might be.
Another thing to check is that if you hook up code to callbacks on that serial port, make sure none of them call Unity methods if they aren’t on the main thread. Apparently you CAN call Debug.Log() off the main thread, even if the docs don’t promise it will work.
Since IL2CPP currently strips out all the line numbers and addresses, you get to do it the hard way with “debug printfs” as we used to call it, or basically logging. Yay IL2CPP!!!
Alternately, make a development build and attach the debugger!
Either way, in the off chance it is a build error, here’s the usual list:
How to troubleshoot build failures:
Obviously, if there is actionable data, clues or information within any of the errors, fix those problems. Each error entry may have more information than can fit in the console log so select each error and read the expanded view below it.
If that gives you nothing worthwhile (look to Google! You’re never the first one!), then…
First, make a blank project with a single blank scene and prove that it builds successfully.
If the blank project does NOT build, go fix your Unity installation or your other tools, such as Android SDK, NDK, JDK, etc. It may even be necessary to change to a different version of Unity3D. It is generally best to stay with LTS versions of Unity3D.
Until you can build a blank project to the target platform, don’t fiddle with anything else.
Once you can build a blank project, now bisect the problem by bringing over parts of your current project and building it one subsystem at a time, perhaps stubbing things out that might trigger compiler errors.
Most often things that prevent building are third-party libraries such as Firebase.
Once you identify the subsystem, go to the documentation for it and make sure you are doing it correctly.
It may also be helpful to work through a tutorial or two for whatever subsystem is making the build fail.
Android build not building:
Circa July 2022 here have been reports of Unity’s installer failing to install the Android Tools.
Here was how I brought up Unity2020.3.41 and the Android SDK 31 on October 30, 2022 (edited on August 23, 2023 to include Android SDK 33…) (and again for SDK34):
Android Gradle errors and other related stuff: