I saw a project get themselves in that position by using a lot of AWS services. At some point it seems they had a dev environment but it quickly faded.

Their solution was to have an anonymized copy of prod to a few (like 3 for 20 engineers) environment where features could be tested. Engineers usually paired in order use them concurrently for unrelated features and they were very expensive.

I did not live enough to see the on-demand environments arrive - devops was always busy with operations tickets to continue building those.