In the general case, the fewer forms you have the higher the conversion rate. However, if the form lacks important information for the users, like trust signals or other specific info, your completion rate will drop.
One thing at a time is much easier for the brain to process.
"Two stimuli therfore achieve worse results than just one. It seems
contrary to common sense, but we believe that the reason for it is
that the brain wants to save energy,"
Germund Hesslow, Source
That's why when we are presented with one complex and one simple task most of the times we prefer to do the simple one. That's because our brain is constantly trying to save precious energy. In our case if we have two forms we should process twice as much information as with one form. On a low processing level the brain will prefer to process one stimulus instead of more. Our brain likes simple stuff.
There are a number of studies exploring this question. You can search google with this query for more.
In general, the fewer forms you have, the higher your conversion rate.
As you can see from the articles that you've linked, they all advise reducing the number of registration form fields.
A study by Oracle's Egan Cheung based on 1500 forms found almost a linear relationship between the number forms and the conversion rate:
However, other study by vwo found that removing too much information from the form might yield a lower conversion rate. In one of the variants they stripped down a 3 form field and got 10% better conversion rate than the control version. However, when they trimmed more forms and removed navigation they got only 2.78% better conversion rate than the control.
Test for missing information
Because your interface is different than those in the studies above your results will be different. You should test what happens in your specific case. The result from the last study shows that sometimes you might trim valuable information that users need. Therefore, you should test if your form lacks some information that's crucial to users.
If you can attach conversion rate tracking to the form, then create different variations and compare them using A/B testing: you will receive valid, objective data. User tests will also help a lot in answering your question.