I have not been programming with Unity for a long time. But I was struck by the "build" process In an important project, "build" takes about 25 minutes. If I make a minimum modification in the code (even if it's just a line) and I have to re-build the project ... another 25 minutes. I might do something wrong since I can not believe this process is like that. I understand that the most practical thing would be for the cache to identify the changes (at least in "shaders", which is what it takes the most) and if there are no modifications, ignore them. That's why I think I do not do something right and ask the forum for help. Thank you.
Creating asmdef files is the easiest way to improve build performance. http://www.screaminggoose.com/blog/2019/2/4/how-i-cut-unity-compile-times-by-75 https://docs.unity3d.com/2018.3/Documentation/Manual/ScriptCompilationAssemblyDefinitionFiles.html
Asmdef files will help with compilation performance, but that's not usually the biggest part of the overall project build - usually it is more the content that takes the time. You can speed up content build by learning to use Asset Bundles, because when your content is in an Asset Bundle then it doesn't need to be rebuilt every time you build your project, it only needs to be rebuilt when you actually changed something in the bundle. The Addressables package provides a layer on top of Asset Bundles which should make using them quite easy.