So you want to advance to a higher level and have a broad interests?

You failed some MS cert exam?

You have a review coming up?

Broad interests. Don't miss the forest for the trees. Learn core concepts and things that are useful in many contexts rather than specifics. This is where a lot of newbies go wrong. E.g. don't learn about AD, learn LDAP and AD, OpenLDAP, DS389, will all come much easier. In most roles some basic programming with Python will come in handy. Once you learn to write code in one language, learning others comes a lot faster. Some worthwhile things to have a foundational grasp of: PKI and how it is used by SSH and TLS, a high level understanding of common network protocols. Peruse IETF RFCs for that. E.g. if you know how say DNS works, you can manage it using any DNS server software. Ditto http and web servers. You will need to learn configuration management SW and monitoring SW. I prefer salt stack and zabbix. There are many good choices.

Seriously learn PKI and TLS. I can recommend some good sources. TLS is used by pretty much everything to secure connections. Backup server to agent, browser to web server, AV to server, you name it.

Open Source is your friend, learn a bit about big projects. E.g. say you get good with backups and want to work for your favorite product vendor. That fancy backup appliance or cloud service is probably running Linux or FreeBSD on the metal and using something like Tomcat for the WebUI.

Learn a bit about licensing models. You will have to deal with it no matter what path you choose.

I wouldn't try to impress your supervisor. Chances are, they'll see through it. They may or may not care about their employees. Assume they don't. Don't assume the worst either. You can almost always trust interests. Their job in an MSP environment is to make sure contractual requirements are met and clients are happy. Focus on where your interests are aligned. Happy clients mean less headaches for you and your boss. I would let them lead the conversation, but focus on that aspect. If a lot of clients use X thing, mention that to your boss that you want to learn more about X thing as it will help you close tickets faster.