MIA TRACON Controller reported a potential loss of separation between two aircraft at a hotspot for VFR traffic near the OPF airport.

Narrative

Aircraft X was inbound to OPF from the northwest; they requested Runway 12. I got them down to 020 to get under MIA approach traffic and put them on a vector southwest-bound for sequence. I then turned [them on a] 100 heading to intercept the localizer because there was a VFR at 019 a mile west of the localizer heading northwest-bound. The area where this happened is usually a hotspot for VFR traffic in the way of descending IFR traffic. Right as Aircraft X was about to intercept the localizer; the VFR turned north right into his path. Aircraft X was about to turn southeast on the intercept and the VFR was 100 ft. under him - if Mode C was correct - so; my immediate thought was to climb Aircraft X to 025. There was traffic; Aircraft Y; westbound in the downwind about 6 miles away at 030. I tried to climb him to 035; but was stepped on by Aircraft X saying he had the VFR in sight and no factor. I told Aircraft X to descend back down to 020 for the approach and called the IFR traffic. I then climbed Aircraft Y to 035 and called the traffic. Due to clouds; visual separation could not be achieved. As lateral separation was lost; altitude started to correct. The area this occurred is a hotspot for VFR traffic. There aren't many ways to safely descend IFR traffic down to 020 when getting them into OPF; but it has to be accomplished to get under inbounds to MIA descending to 030. The pilots who are VFR in the area need to be more alert and aware that there is usually jet or turboprop traffic.