What finally worked for me was the following:
1) Install Java 21 and Java 64; both if a 64-bit machine).
2) Using Firefox, and get into sweethome
3) use the "ONLINE". This will fire-up JAVA
4) leave Firefox ON, minimize window, and fireup the installed local Sweethome program.
Weird as it sounds, but that works. For Java, use the "offline"installations https://java.com/en/download/manual.jsp
The install will clear up old and unneeded versions.Enable Java (from the Configure java app)