@TimO Ok, found it. This was the problem:
#define MY_CONTROLLER_IP_ADDRESS 192, 168, 80, 190
After disabling UDP in the sketch, this UDP-specific line should have been outcommented too.
Openhab log looks fine:
2020-10-21 15:23:15.294 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model 'demo.things'
2020-10-21 15:23:15.872 [INFO ] [thome.model.lsp.internal.ModelServer] - Started Language Server Protocol (LSP) service on port 5007
2020-10-21 15:23:16.277 [INFO ] [.dashboard.internal.DashboardService] - Started Dashboard at http://192.168.80.190:8080
2020-10-21 15:23:16.308 [INFO ] [.dashboard.internal.DashboardService] - Started Dashboard at https://192.168.80.190:8443
2020-10-21 15:23:16.606 [INFO ] [panel.internal.HABPanelDashboardTile] - Started HABPanel at /habpanel
2020-10-21 15:23:16.621 [INFO ] [ebuilder.internal.HomeBuilderServlet] - Started Home Builder at /homebuilder
2020-10-21 15:23:16.637 [INFO ] [openhab.ui.paper.internal.PaperUIApp] - Started Paper UI at /paperui
2020-10-21 15:23:16.918 [DEBUG] [nsors.handler.MySensorsBridgeHandler] - Initialization of the MySensors bridge
2020-10-21 15:23:16.949 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Cache file: given_ids.cached exist.
2020-10-21 15:23:16.949 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Cache (given_ids) content: []
2020-10-21 15:23:16.949 [DEBUG] [al.protocol.ip.MySensorsIpConnection] - Enabling connection watchdog
2020-10-21 15:23:16.949 [DEBUG] [nsors.handler.MySensorsBridgeHandler] - Initialization of the MySensors bridge DONE!
2020-10-21 15:23:16.949 [DEBUG] [.discovery.MySensorsDiscoveryService] - Starting MySensors discovery scan
2020-10-21 15:23:16.965 [DEBUG] [al.protocol.ip.MySensorsIpConnection] - Connecting to IP bridge [192.168.80.185:5003]
2020-10-21 15:23:17.262 [DEBUG] [rsAbstractConnection$MySensorsWriter] - Sending to MySensors: 0;0;3;0;2;
2020-10-21 15:23:17.292 [DEBUG] [rsAbstractConnection$MySensorsReader] - Message from gateway received: 0;255;3;0;14;Gateway startup complete.
2020-10-21 15:23:17.309 [DEBUG] [rsAbstractConnection$MySensorsReader] - Message from gateway received: 0;255;0;0;18;2.3.2
2020-10-21 15:23:17.309 [DEBUG] [rs.internal.gateway.MySensorsGateway] - Presentation Message received
2020-10-21 15:23:17.309 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Writing on cache given_ids, content: [0]
2020-10-21 15:23:17.309 [WARN ] [.discovery.MySensorsDiscoveryService] - Cannot automatic discover thing node: 0, child: 255 please insert it manually
2020-10-21 15:23:17.309 [DEBUG] [rsAbstractConnection$MySensorsReader] - Message from gateway received: 0;255;3;0;2;2.3.2
2020-10-21 15:23:17.309 [DEBUG] [rsAbstractConnection$MySensorsReader] - Good,Gateway is up and running! (Ver:2.3.2)
2020-10-21 15:23:17.309 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Writing on cache given_ids, content: [0]
2020-10-21 15:23:17.309 [INFO ] [al.protocol.ip.MySensorsIpConnection] - Successfully connected to MySensors Bridge.
and the gateway's debug output also looks fine:
15:22:53.667 -> 0 MCO:BGN:INIT GW,CP=RSNGA---,FQ=16,REL=255,VER=2.3.2
15:22:53.667 -> 4 TSM:INIT
15:22:53.667 -> 5 TSF:WUR:MS=0
15:22:53.667 -> 7 TSM:INIT:TSP OK
15:22:53.667 -> 8 TSM:INIT:GW MODE
15:22:53.667 -> 10 TSM:READY:ID=0,PAR=0,DIS=0
15:22:53.667 -> 12 MCO:REG:NOT NEEDED
15:22:54.236 -> 575 GWT:TIN:IP=192.168.80.185
15:22:55.257 -> 1579 MCO:BGN:STP
15:22:55.257 -> 1580 MCO:BGN:INIT OK,TSP=1
15:22:55.257 -> 1583 TSM:READY:NWD REQ
15:22:55.257 -> 1586 ?TSF:MSG:SEND,0-0-255-255,s=255,c=3,t=20,pt=0,l=0,sg=0,ft=0,st=OK:
15:23:17.292 -> 23449 GWT:TSA:ETH OK
15:23:17.292 -> 23453 GWT:RFC:MSG=0;0;3;0;2;
15:23:17.292 -> 23457 GWT:RFC:MSG=
15:23:17.292 -> 23459 GWT:RFC:MSG=
Thanks for your time and patience to a newbie!