it looks there is an issue with the official SDK package. When trying to download it in a new installation I got this:
Downloading boards definitions.
2021-01-20T18:50:45.355Z INFO c.a.u.n.FileDownloaderCache:131 [main] The cache is not enable.
2021-01-20T18:50:45.364Z INFO c.a.u.n.HttpConnectionManager:153 [main] Connect to https://github.com/bigjosh/Move38-Arduino-Platform/releases/download/1.2/Move38-Arduino-Platform-main.zip, method=GET, request id=F450CB20DACC4E6C
2021-01-20T18:50:45.932Z INFO c.a.u.n.HttpConnectionManager:157 [main] Request complete URL="https://github.com/bigjosh/Move38-Arduino-Platform/releases/download/1.2/Move38-Arduino-Platform-main.zip", method=GET, response code=206, request id=F450CB20DACC4E6C, headers={Accept-Ranges=[bytes], null=[HTTP/1.1 206 Partial Content], Server=[AmazonS3], Content-Range=[bytes 0-1332526/1332527], ETag=["f9c91263d73c0db5c9d2719fd0603723"], Content-Disposition=[attachment; filename=Move38-Arduino-Platform-main.zip], Last-Modified=[Wed, 16 Sep 2020 04:04:40 GMT], x-amz-request-id=[4F96F3823418ABEF], Content-Length=[1332527], x-amz-id-2=[6UQPNMvAZV+y9w5HMFvx6BeN5jysSAF0dtEUpGDohyPWPkS9fQENpFNPkYtn9n8GCbzpwh9jsiA=], Date=[Wed, 20 Jan 2021 18:50:46 GMT], Content-Type=[application/octet-stream]}
Downloading boards definitions. Downloaded 1,332kb of 2,665kb.
Downloading boards definitions. Downloaded 1,359kb of 2,665kb.
Downloading boards definitions. Downloaded 1,394kb of 2,665kb.
Downloading boards definitions. Downloaded 1,429kb of 2,665kb.
Downloading boards definitions. Downloaded 1,464kb of 2,665kb.
Downloading boards definitions. Downloaded 1,498kb of 2,665kb.
Downloading boards definitions. Downloaded 1,533kb of 2,665kb.
Downloading boards definitions. Downloaded 1,568kb of 2,665kb.
Downloading boards definitions. Downloaded 1,603kb of 2,665kb.
Downloading boards definitions. Downloaded 1,638kb of 2,665kb.
Downloading boards definitions. Downloaded 1,673kb of 2,665kb.
Downloading boards definitions. Downloaded 1,707kb of 2,665kb.
Downloading boards definitions. Downloaded 1,742kb of 2,665kb.
Downloading boards definitions. Downloaded 1,777kb of 2,665kb.
Downloading boards definitions. Downloaded 1,812kb of 2,665kb.
Downloading boards definitions. Downloaded 1,847kb of 2,665kb.
Downloading boards definitions. Downloaded 1,881kb of 2,665kb.
Downloading boards definitions. Downloaded 1,916kb of 2,665kb.
Downloading boards definitions. Downloaded 1,951kb of 2,665kb.
Downloading boards definitions. Downloaded 1,986kb of 2,665kb.
Downloading boards definitions. Downloaded 2,021kb of 2,665kb.
Downloading boards definitions. Downloaded 2,055kb of 2,665kb.
Downloading boards definitions. Downloaded 2,090kb of 2,665kb.
Downloading boards definitions. Downloaded 2,125kb of 2,665kb.
Downloading boards definitions. Downloaded 2,160kb of 2,665kb.
Downloading boards definitions. Downloaded 2,195kb of 2,665kb.
Downloading boards definitions. Downloaded 2,230kb of 2,665kb.
Downloading boards definitions. Downloaded 2,264kb of 2,665kb.
Downloading boards definitions. Downloaded 2,299kb of 2,665kb.
Downloading boards definitions. Downloaded 2,334kb of 2,665kb.
Downloading boards definitions. Downloaded 2,369kb of 2,665kb.
Downloading boards definitions. Downloaded 2,404kb of 2,665kb.
Downloading boards definitions. Downloaded 2,438kb of 2,665kb.
Downloading boards definitions. Downloaded 2,473kb of 2,665kb.
Downloading boards definitions. Downloaded 2,508kb of 2,665kb.
Downloading boards definitions. Downloaded 2,543kb of 2,665kb.
Downloading boards definitions. Downloaded 2,578kb of 2,665kb.
Downloading boards definitions. Downloaded 2,613kb of 2,665kb.
Downloading boards definitions. Downloaded 2,647kb of 2,665kb.
Verifying archive integrity...
java.lang.Exception: CRC doesn't match, file is corrupted. It may be a temporary problem, please retry later.
at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:105)
at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:60)
at cc.arduino.contributions.packages.ContributionInstaller.install(ContributionInstaller.java:105)
at processing.app.Base.<init>(Base.java:348)
at processing.app.Base.main(Base.java:150)
[Error] Exit with code=255
Maybe the actual package was updated without the json file being updated?