This is really weird. Armory does not access the WAN at all. It only talks to your node on localhost. If your node is seeing Armory, broadcast should work. Maybe your settings prevent tx relay? Or "onlynet=onion" is rejecting the connection from localhost, which is not correctly reflected in the node count. At any rate, you can copy the raw tx from Armory and broadcast it directly with Core.
I checked the log file and found this...
2021-11-26 16:02:44 (INFO) -- ArmoryQt.py:1872 - setSatoshiPaths
2021-11-26 16:02:44 (WARNING) -- SDM.py:402 - Spawning DB with command: ArmoryDB --db-type="DB_FULL" --cookie --satoshi-datadir="/home/xxx/.bitcoin/blocks" --satoshi-port=8333 --datadir="/home/xxx/.armory/" --dbdir="/home/xxx/.armory/databases"
2021-11-26 16:02:44 (INFO) -- ArmoryUtils.py:689 - Executing popen: ['ArmoryDB', '--db-type="DB_FULL"', '--cookie', '--satoshi-datadir="/home/xxx/.bitcoin/blocks"', '--satoshi-port=8333', '--datadir="/home/xxx/.armory/"', '--dbdir="/home/xxx/.armory/databases"']
2021-11-26 16:02:44 (INFO) -- ArmoryQt.py:1824 - Connecting on port 50559
This is were Armory connects to the WAN I guess.
I deleted the onlynet=onion option but it didn't help. Maybe its due to the proxy settings
Can you point me somewhere where I can find an explanation how to broadcast an armory-transaction directly with Core?
Cheers for your help!