I'm a huge fan of romance trilogies, and I've spent a lot of time digging into whether my favorites have sequels. For example, after the 'Before' trilogy ('Before Sunrise', 'Before Sunset', 'Before Midnight'), there hasn't been any official announcement about a fourth movie, though fans keep hoping. Another one is the 'After' series, which actually expanded beyond the original trilogy with 'After We Fell', 'After Ever Happy', and even more adaptations planned from the books.
Some trilogies, like 'Fifty Shades of Grey', wrapped up their main story but spawned spin-offs like 'Fifty Shades Freed'. It really depends on the franchise. If you're curious about a specific trilogy, checking the author's or studio's social media often gives the latest updates.