setfilter doesnt work with more than 3 filters

hello , i was really working on this for a long time, its just the same setfilter that anybody works with, everytime i try to add one after the third filter, it just doesnt work, can somebody helps me find a way to add more than 3 filters with setfilter ? and thank you in advance

export function searchbutton_click(event) {
 let filter = wixData.filter()

// add another condition and keep old filters

// conditional filter

    filter = filter.eq('age', Number($w('#age').value))

    filter = filter.contains("fullName", $w('#name').value)
    filter = filter.contains("country", $w('#country').value)
    filter = filter.contains("position", $w('#position').value)
    filter = filter.contains("glet", $w('#glet').value)

// finally, we set the filter

Please explain what works, which filters work and how, and what doesn’t work.