If it was working “fine” then why was Iran able to reach 60% enriched uranium and enough for 10 nuclear weapons if they were able to enrich further?

That enrichment occurred after Trump voluntarily exited the JCPOA. The IAEA reported no enrichment over the 3.67% threshold through 2018, then reported over 400kg at 60% in 2025, all created in the period after Trump pulled out. You are describing a consequence of ending the JCPOA.