Best Way to Gain Off-Page & Technical SEO Experience

I’ve been working at a small SEO agency for the past 3 years that’s extremely hit or miss with its work quality. I’ve been looking for a new company for awhile now but keep running into the same issue, a lack of off-page and technical SEO experience. My current company only really focuses on on-page SEO with programmers handling small amounts of off-page and technical SEO, which means I have a massive gap in my resume that’s already made me lose out on a few job opportunities. Normally I would ask our programmers to teach me, but the owner of the company doesn’t want any SEO managers to touch the back end of client websites, so only the programmers can handle that part. Is there a good way for me to learn more about these parts of SEO or get some actual hands-on experience with them?