Library Manager Error Downloading library_index on Mac

I always get the message " Error downloading https://downloads.arduino.cc/libraries/library_index.json" on Mac Big Sur with Arduino 1.8.13. Won’t download any libraries either, with a corresponding message. I’m starting a new thread because previous solutions didn’t help. I can access the subject file from my browser, and an older one does exist in ~Library/Arduino15 and Arduino preferences are set to auto-detect proxy settings with the URL box unchecked. Message is

java.lang.RuntimeException: java.lang.Exception: Error downloading https://downloads.arduino.cc/libraries/library_index.json
	at cc.arduino.contributions.libraries.ui.LibraryManagerUI.lambda$onUpdatePressed$2(LibraryManagerUI.java:207)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.Exception: Error downloading https://downloads.arduino.cc/libraries/library_index.json
	at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:149)
	at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:130)
	at cc.arduino.contributions.JsonDownloader.download(JsonDownloader.java:49)
	at cc.arduino.contributions.GZippedJsonDownloader.download(GZippedJsonDownloader.java:66)
	at cc.arduino.contributions.libraries.LibraryInstaller.updateIndex(LibraryInstaller.java:84)
	at cc.arduino.contributions.libraries.ui.LibraryManagerUI.lambda$onUpdatePressed$2(LibraryManagerUI.java:203)
	... 1 more
Caused by: java.net.SocketException: Socket closed
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:476)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:218)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:200)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:394)
	at java.net.Socket.connect(Socket.java:606)
	at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:287)
	at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
	at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:292)
	at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:395)
	at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191)
	at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1205)
	at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
	at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177)
	at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:167)
	at cc.arduino.utils.network.HttpConnectionManager.makeConnection(HttpConnectionManager.java:155)
	at cc.arduino.utils.network.HttpConnectionManager.makeConnection(HttpConnectionManager.java:106)
	at cc.arduino.utils.network.FileDownloaderCache.updateCacheInfo(FileDownloaderCache.java:184)
	at cc.arduino.utils.network.FileDownloaderCache.getFileCached(FileDownloaderCache.java:153)
	at cc.arduino.utils.network.FileDownloader.downloadFile(FileDownloader.java:167)
	at cc.arduino.utils.network.FileDownloader.download(FileDownloader.java:129)
	at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:147)
	... 6 more

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