@borkdude to answer the deleted q - min supported version is 1.7: https://github.com/jonase/eastwood/blob/4c6b01f1926c91f9f8452568b5385f2fa56f88bf/.circleci/config.yml#L351
I deleted the question because it turned out the incompatiblity was elsewhere (tools.deps.alpha). thanks for answering.
clj-kondo depends on tools.deps.alpha in tests. when running the tests with 1.9 this is a bit inconvenient since I have to use a very old version which doesn't use requiring-resolve