[usaphp]

Have you tried managing it using https://managewp.com? I was in your shoes and it saved me a lot of headache

[knowsmorsecode]

So you allow managewp to login to your sites?

[usaphp]

It uses official WordPress Rest API: https://developer.wordpress.org/rest-api/

[analogmemory]

ManageWP uses the WordPress api to update plugins and themes