it's not the db, must be an incompatibility between desktop 1.2.4 and 4.0.0:
db in 4.0.0 had been force-imported from 3.5.14 version -> error
db can be dumped from 4.0.0 version, a reload today -> same error
force-imported the 3.5.14 dump to a new db works fine.
In my copy above I had not copied the two warnings bevore the logged error:
2020-01-17 08:21:19.873+0000 WARN Use of deprecated setting dbms.active_database. It is replaced by dbms.default_database 2020-01-17 08:21:19.877+0000 WARN Unrecognized setting. No declared setting with name: dbms.connector.bolt.address
perhaps there's some inconsistency in the 4.0.0 version I had simply upgraded.
BTW, first start of 4.0.0 necessitated java 11 with JAVA_HOME set, which my old java 8 hadn't.