As a young, inexperienced teacher I found Faith Builder’s Summer Term (5 weeks during the month of July) quite formative. You can find out more here: https://fbep.org/st. If you’re looking something shorter you could consider Teacher’s Week during the first week of August.
I also recently saw a flyer in our school office advertising teacher training sessions offered by CLE. These are one week long, and take place at various locations throughout the country. This may less helpful if your school does not use their publications.
We are often given a book to read, digest, and discuss over the summer. I think this is a significant way to improve professional development as a teacher. Two books that were influential for me were, Teach Like a Champion by Doug Lemov and The 7 Habits of Highly Effective People by Stephen Covey.