Alright spun up an example using Ubuntu 20.04:
Root Domain: http://strapi.guru (with a little hi messages 
)
API (Articles): http://strapi.guru/api/articles
Admin Panel: http://strapi.guru/api/admin ( username: test@test.com, password: Test1234!)
I’ve also taken the liberty of symlinking some of the config files into the public directory so you can see them directly:
/etc/nginx/sites-enabled/strapi.conf => http://strapi.guru/api/strapi.conf
/etc/nginx/conf.d/upstream.conf => http://strapi.guru/api/upstream.conf
/srv/strapi/testProxy/config/env/production/server.js => http://strapi.guru/api/server.js
Other than that I did zero other configuration of the droplet, simply installed the dependencies, created a Strapi app, configured Strapi and Nginx, started Strapi with pm2 and reloaded Nginx.
If you want I can test the sub-folder split also instead of just the unified.
Here is a sample of the logs:
And proof of the machine, is what I claim it to be:
