Well, Xojo has made tons of changes to the languaje itself without real functionality improvemt. This changes have rendered almost all resources useless.
At some point some third party sites ofered Xojo traingin, but with this constant changes and the small comunity, was not worth it update the materials, for example: https://forum.xojo.com/t/bkeeney-and-bkeeneybriefs-are-going-away/63500
This have the same problem, most of the previous magazine issues samples are outdated.
This tutorials are up to date, but are very basic concepts for beginers: