Exhaust fan venting through soffit where attic has no vent
Avoiding penetrating the roof with a bath fan vent is the wrong disposition.  Given current materials and techniques, a weather tight seal can be expected every time.  And the trade-off is clearly on that side. Their just too many risks when dumping the vent fan anyplace but through the roof. Keep the run as short as possible and as vertical as possible.  Happy venting.