If you want a similar 3D Sonic experience on PSP, the closest official games are:
An official Sonic Unleashed ROM for the PlayStation Portable (PSP) does not exist because the game was never released for that platform. While the game launched in 2008 for the PlayStation 2, PlayStation 3, Xbox 360, and Wii, a handheld PSP version was never developed or published by SEGA. Sonic Unleashed Psp Rom
No. Sonic Unwiished (fan name) refers to the Wii/PS2 versions, which have 3D hub worlds and different level geometry. The PSP version is its own 2D engine. If you want a similar 3D Sonic experience
Because no official ROM exists, any "Sonic Unleashed PSP ROM" found online is typically one of the following: Fan-Made Demakes : Community projects, such as those featured on Sonic Fan Games HQ , often attempt to recreate the "Boost" gameplay of using the PSP's aesthetic or engines like Unity. PS Vita Fan Ports Sonic Unwiished (fan name) refers to the Wii/PS2
It's essential to understand that downloading ROMs of games you do not own can be illegal in many jurisdictions. The legality often hinges on whether the individual owns a physical or digital copy of the game. Supporting game developers by purchasing their titles is a straightforward way to enjoy games legally.