I’d recommend Wordpress both if you are planning on using it as a service for clients or building your own site.
Squarespace is great for getting stuff live quickly and easily, but against competitive search terms, it’s SEO isn’t great. So you’ll have a great looking site, but no visitors! Not every VA will be wanting to pull visitors from Google, but if that is your plan, make sure it’s on an SEO friendly platform.
Our local council runs a really good Wordpress course - designed for people building their own, but the tech stuff in it is really good. Most clients would ask a VA to make changes, do simple keyword optimisation, schedule blogs, add pics, run backups etc. but would get a web developer in for the more advanced stuff.
The Digital Mums courses always get good reviews?