Men & Women Mixing

Seclusion (الخلوة) (being alone) with a stranger of the opposite gender is strictly forbidden.
It’s a sin and can lead to Fahshaa.
However, mixing (الاختلاط) in public places or in the presence of other people – when the correct Hijab is observed and there is no fear of Fitnah – that’s not a problem.

Imam Malik was asked:
قَالَ يَحْيَى: سُئِلَ مَالِكٌ: هَلْ تَأْكُلُ الْمَرْأَةُ مَعَ غَيْرِ ذِي مَحْرَمٍ مِنْهَا أَوْ مَعَ غُلَامِهَا؟ فَقَالَ مَالِكٌ: ” لَيْسَ بِذَلِكَ بَأْسٌ، إِذَا كَانَ ذَلِكَ عَلَى وَجْهِ مَا يُعْرَفُ لِلْمَرْأَةِ أَنْ تَأْكُلَ مَعَهُ مِنَ الرِّجَالِ
قَالَ: وَقَدْ تَأْكُلُ الْمَرْأَةُ مَعَ زَوْجِهَا، وَمَعَ غَيْرِهِ مِمَّنْ يُؤَاكِلُهُ، أَوْ مَعَ أَخِيهَا عَلَى مِثْلِ ذَلِكَ، وَيُكْرَهُ لِلْمَرْأَةِ أَنْ تَخْلُوَ مَعَ الرَّجُلِ لَيْسَ بَيْنَهُ وَبَيْنَهَا حُرْمَةٌ ”
“Can a woman eat with other than her relative (maḥram) or slave?”
Imam Malik replied:
“There is no harm in that if it is in a manner which is accepted for a woman to eat with men.
A woman sometimes eats with her husband and with others he dines with or with her brother in the same way.
It is disapproved of for a woman to be alone with a man when there is no relationship between them by blood, marriage or suckling that would prevent him marrying her.”
[“Muwatta Malik”, 49/35].
https://sunnah.com/urn/417680