A 'recreational' solo dive is one that is planned for an open-water, non-ceiling environment, where direct access to the surface is always available. However, one of the primary contingencies that must be addressed by solo divers is the risk that they could be trapped or incapacitated in a way that prevents them reaching the surface immediately. Without assistance from a buddy, they must have the capacity to deal with that situation.
In short:
Technical Solo Dive: Deliberate planning for operation in an over-head (virtual/physical) environment.
Recreational Solo Dive: Contingency preparation for being denied immediate access to the surface.
The same diver capability and equipment redundancy needs to exist, whether obstruction from the surface is a planned objective or a contingency preparation.
Historically, formal training to provide that capability has derived from technical diving programs.
In practical terms, that training (regardless of where it is 'book-shelved') is at a 'technical' level, in respect of skill-set, capability and mind-set.