Exploring best way to get into assisting with IT server management

Hello,

I am the unofficial IT manager, in training to take over most responsibilities from our IT Consultant.

We have 3 physical locations (soon to be 4) where we have site Dell domain servers running MS Server 2019, along with a few file servers.

Besides office personnel, we have field personnel that VPN's into our systems, with a mix of Win 10 Pro and Win 11 Pro installations.

What courses or route of learning would be best for me to assist with profiles and active directory, overall server setup (for any new sites as we expand) and server management, security, and all related?

Apologies if this is a basic question that others might have a simple answer for.

My current level of IT is network amateur: I've installed small networks without server, supervised servers (not technically 'managed'), built PCs, did basic/intermediate troubleshooting for PCs and network (mostly by googling and other research).

Any pointers would be appreciated.