In order for someone to help you with API Request questions, it is critical that you post here the API Request you are using.
Remember to replace your Key with [THE_KEY].

So we can better understand what your goal is.
It is not one of the options of the multi search Request.
But you can experiment and test.
In this test I did it had an effect. The popularity was respected.

https://api.themoviedb.org/3/search/multi?api_key=[THE_KEY]&language=en-US&query=Jack%20Reacher&page=1&region=US&sort_by=popularity.desc  
https://api.themoviedb.org/3/search/multi?api_key=[THE_KEY]&language=en-US&query=Jack%20Reacher&page=1&region=US&sort_by=popularity.asc

Hi @ticao2 , thanks for your answer.

You are right, I should have posted the url for the API request. Anyway I tested the query as you suggested and it's working totally fine.

Thank you!

@ticao2 said:

In this test I did it had an effect. The popularity was respected.

https://api.themoviedb.org/3/search/multi?api_key=[THE_KEY]&language=en-US&query=Jack%20Reacher&page=1®ion=US&sort_by=popularity.desc  
https://api.themoviedb.org/3/search/multi?api_key=[THE_KEY]&language=en-US&query=Jack%20Reacher&page=1®ion=US&sort_by=popularity.asc

Hi,

5 years later it seems to popularity is not respected. Both request return:

... | jq .results[].popularity
8.5005
1.3046
11.6605
68.6087

Could you help me how to search people most popular first?

Bert Regards, rysson.

Hi @rysson,

None of our search methods support a custom sort option. They are designed to try and return the most relevant results (and to be boosted by popularity) but there is no way to use a custom sort option.

OK, thank you for response.

It means that I need to wait Clint Eastwood will be boosted. Now the first person is 2189663, noname Eastwood, with no any date filled yet. 😋

 http api.themoviedb.org/3/search/person language==en-US query=='eastwood' region==US | jq .results[].popularity
0.0388
0.0819
4.3813

It's clear the sort method is not supported. It will be break cache and performance. I understand it.

Good luck,

rysson