Hello Mona and first of all thanks for your reply.
I immediatly tried your solution but I receive different errors.
The Choices function in the ComboBox works fine, so I see the values I see in Sharepoint.
When apply the filter something does not work and selecting any values fomr the ComboBox do nothing, below my Combobox formula where SIIndustry is the Choice type column in Sharepoint with multi selection option.
Choices('Omron System Integrator List'.SIIndustry)
Than the filter below:
Filter('Omron System Integrator List',First(ComboBox3.SelectedItems) in SIIndustry && Last(FirstN(ComboBox3.SelectedItems,2)) in SIIndustry &&Last(FirstN((ComboBox3.SelectedItems,3)))