Since the new launcher beta (2.3.481) Forge modded installations do not start at all anymore. Some throw up error code 1 while others don't even attempt to start (See screenshots). This is only the case with Forge, other modded installations like Fabric or Optifine are not affected.

Not sure if this is a launcher issue or rather a Forge issue, but figured I'd start here.

Note that this issue only affects beta 2.3.481, not any other version. I wasn't able to select that version though, so I chose the newest available one.