entrypoint is the command , CMD is for argument

https://www.ctl.io/developers/blog/post/dockerfile-entrypoint-vs-cmd/

but you want run run entrypoint.sh then start.sh, here is the tricks

ENTRYPOINT ["/entrypoint.sh"]
some code or not...
CMD ["/start.sh"]

entrypoint.sh:

some code for entrypoint ...
exec "$@"

using exec, the start.sh (as parameter) will run

CODE