What I am looking for is "When we conduct a systematic review and we found for example 60 relevant studies. Should we list them in the reference list? " or just mention the number?
All the 60 studies (for example) have been mention as studies dealt with the aim of the systematic review. That means all of them have been investigated at least the abstract and/or the aim. So should the study's references list includes all of them? unfortunately still not clear for me
The systematic review or (review papers) means you are searching , all possible references studying the desired subject. Listing all this references is a necessary condition to publish your work. So, yes you should list them in the references list.
For the sake of transparency, you may list them either in the article or in the appendix, but you are not obliged (as I can see in many published articles).
Anyways, in the findings section, you have to cite around 70% of the articles that you have selected (about 40 articles in your example).
If your systematic review includes 120 papers but the journal only allows 80 references, what can be done? (assuming that it is not possible to further restrict the exclusion criteria)