Selecting features from table A using table B

SELECTION.sql

-- Expression to be used at SELECT BY EXPRESSION AT LAYER A

array_contains( -- This will return true if the array contains the value
    aggregate( -- will aggregate all values from target in to a string, using semicolons as concatenator
        layer:='<table_b>', --  Target table containing the values, replace <table_b> whith your table name
        aggregate:='array_agg',
        expression:=to_string("<field_from_table_b>"), -- Field from table_b containing the values
     ),
"<field_table_a>") -- Field from table a with values to compare, replace <field_table_a> with your field name

Thx @pigreco for the last revision tip....
I always forget the 'array_agg'.