Did I read somewhere that there is a SLF4J 2.x compatibility module that will provide StaticLoggerBinder to keep old applications from breaking? I thought I had read that somewhere, but I can't find it now.

If there is no such thing, then I propose that a separate SLF4J 2.x library be published as a sort of "migration bridge" between SLF4J 1.x and SLF4J 2.x. It would provide a minimal StaticLoggerBinder that doesn't allow registration of any modules, but would implement getLoggerFactory() to delegate to the default version. This would allow an application to manually pull in SLF4J 2.x, but still not crash when a misbehaving application such as Spark 3.3.0 tries to access StaticLoggerBinder manually. (See SPARK-40489.) This would just be a single artifact to include as a dependency to keep legacy classes from breaking.

If you're not open to that suggestion, I suppose I could create such a "bridge" as part of my Clogr, but my first choice would be for it to be part of official SLF4J.

Without such a thing, I fear SLF4J 2.x adoption could be slowed. See also SLF4J-562.