One of the most-common things to take a ton of time is baking lightmaps.
One way around this is to bake the lights manually, then commit them to your source control, even though they are HUGE files generally speaking.
Another way to test the theory is to turn OFF light baking in all your scenes, see if that helps.
There’s also the chance that there is a legitimate problem with the project, so some other steps to try are:
- isolate some scenes (remove half, then remove half again, etc.)
- add an empty single scene and try building with that only, etc.
And here’s the obligatory general blurb:
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 misconfigured or incorrectly-installed or incompatible third-party libraries such as Firebase or AdMob or IronSource.
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:
Android SDK35 stuff: