I am seeing a similar issue. When I tried to add SparkFun Apollo3 Boards using the Arduino boards manager, I get the following error:
Error downloading https://github.com/sparkfun/Arduino_Apollo3/releases/download/v2.1.1/Arduino_Apollo3.tar.gz
java.lang.RuntimeException: java.lang.Exception: Error downloading https://github.com/sparkfun/Arduino_Apollo3/releases/download/v2.1.1/Arduino_Apollo3.tar.gz
at cc.arduino.contributions.packages.ui.ContributionManagerUI.lambda$onInstallPressed$2(ContributionManagerUI.java:179)
at java.lang.Thread.run(Thread.java:748)
I have added all of the following URL’s to the boards manager in preferences:
https://raw.githubusercontent.com/sparkfun/Arduino_Apollo3/main/package_sparkfun_apollo3_index.json
Interestingly, I was able to add the Apollo v1.2.3, however I still get the above error when I try to update it to the current version. I also tried uninstalling and re-installing the Arduino IDE, which did not solve the problem.