Proxy through tor does not work on linux

Hey,
I’m using the Nextcloud Desktop Client Version 3.17.3daily and since some time my proxy configuration does not work anymore. I have two Nextcloud instances, that I want to use. One of them is an onion service.

The tor proxy itself is working (127.0.0.1:9050 with socks5), I can use it with other tools. But it does not work with the nextcloud client. If I use the same configuration for the “normal” nextcloud I can sync my files. But I am not sure if the proxy is working here, because the files were synced really fast (tor is normally not fast).

Is it a problem on my side (like the curl RFC7686 DNS issue) or is it a bug?

I have removed the onion account from the client and tried to add it again. But there is nothing happening except for a graphical “Failed to connect” error and these logs:

2025-10-26 15:10:26:998 [ info nextcloud.gui.wizard /usr/src/debug/nextcloud-client/nextcloud-client/src/gui/owncloudsetupwizard.cpp:212 ]:	No system proxy set by OS
2025-10-26 15:10:27:002 [ info nextcloud.sync.accessmanager /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/accessmanager.cpp:72 ]:	2 "" "http://<onionaddress>.onion/status.php" has X-Request-ID "82065b16-225d-4a05-a4eb-8628cbc6e0ed"
2025-10-26 15:10:27:002 [ info nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:363 ]:	OCC::CheckServerJob created for "http://<onionaddress>.onion" + "status.php" "OCC::OwncloudSetupWizard"
2025-10-26 15:10:27:006 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:469 ]:	Network request error "Host <onionaddress>.onion not found" HTTP status 0 httpReason ""
2025-10-26 15:10:27:006 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:214 ]:	QNetworkReply::HostNotFoundError "An unexpected error occurred. Please try syncing again or contact contact your server administrator if the issue continues." QVariant(Invalid)
2025-10-26 15:10:27:006 [ warning nextcloud.sync.networkjob.checkserver /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/networkjobs.cpp:537 ]:	error: status.php replied  0 ""
2025-10-26 15:10:27:006 [ info nextcloud.sync.accessmanager /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/accessmanager.cpp:72 ]:	2 "" "http://<onionaddress>.onion" has X-Request-ID "864b68a9-e7e9-4a13-8ea7-9512dd28b3f7"
2025-10-26 15:10:27:006 [ info nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:363 ]:	OCC::SimpleNetworkJob created for "http://<onionaddress>.onion" + "" ""
2025-10-26 15:10:27:010 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:469 ]:	Network request error "Host <onionaddress>.onion not found" HTTP status 0 httpReason ""
2025-10-26 15:10:27:010 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:214 ]:	QNetworkReply::HostNotFoundError "An unexpected error occurred. Please try syncing again or contact contact your server administrator if the issue continues." QVariant(Invalid)
2025-10-26 15:10:27:010 [ info nextcloud.sync.accessmanager /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/accessmanager.cpp:72 ]:	2 "" "http://<onionaddress>.onion/status.php" has X-Request-ID "5918d462-0351-40cb-9e87-9e8bd0fbd76c"
2025-10-26 15:10:27:011 [ info nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:363 ]:	OCC::CheckServerJob created for "http://<onionaddress>.onion" + "status.php" "OCC::OwncloudSetupWizard"
2025-10-26 15:10:27:014 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:469 ]:	Network request error "Host <onionaddress>.onion not found" HTTP status 0 httpReason ""
2025-10-26 15:10:27:014 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:214 ]:	QNetworkReply::HostNotFoundError "An unexpected error occurred. Please try syncing again or contact contact your server administrator if the issue continues." QVariant(Invalid)
2025-10-26 15:10:27:014 [ warning nextcloud.sync.networkjob.checkserver /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/networkjobs.cpp:537 ]:	error: status.php replied  0 ""
2025-10-26 15:10:27:014 [ warning nextcloud.sync.networkjob /usr/src/debug/nextcloud-client/nextcloud-client/src/libsync/abstractnetworkjob.cpp:469 ]:	Network request error "Host <onionaddress>.onion not found" HTTP status 0 httpReason ""

I have found another thread with someone having the same problem.
So I downgraded to 3.16.6 which helped. But I had to use the global proxy settings. The account based proxy setting do not work either on 3.16.6. The global proxy settings disappeared in 3.17. I think the desktop client is broken.