please address if these “ideas” are actually “trade secrets”

Which ideas? The ones that he was told about as part of the job?

the "technologies and techniques" for which there are "no patents" may still be trade secrets (i.e. confidential information). Depends what they are and the OP hasn't told us.

How would I tell if an idea was a trade secret? If it was created solely by me, not based on any one else’s work, and not (to my knowledge) part of any confidentiality agreement can it be claimed as a trade secret?

@Noxerran - yes it can. If you were employed as, say, a staff writer for the New Yorker then everything you write is their copyright but every idea you have about what to write is their trade secret even if you never write it down.

@DaleM "every idea you have about what to write is their trade secret even if you never write it down". Of course not. The Black's Law Dictionary defines trade-secret as "[a] plan or process [...] known only to its owner and those of his employees to whom it is necessary to confide it". The ideas the OP comes up on his own and kept to himself obviously were not confided to him by the employer (because the OP came up with these on his own). Thus, those ideas cannot constitute employer's trade secret unless the OP contributes them, or makes them known, to the employer.

@IñakiViggers but if the employee is paid to come up with ideas for their employer as creatives are, then the employee’s ideas are the employer’s ideas. The ideas an employee states in, say, a brainstorming session, belong to the employer.

@DaleM "the employee’s ideas are the employer’s ideas". Maybe in theory, but that is hardly enforceable where the employee does not disclose all of his ideas to the employer. There is yet no mind-reading device or method to exhaustively identify which of the employee's ideas fall within scope of the employment agreement and which ones do not.

@IñakiViggers we don’t need mind reading - we have words and ears. If they say it out load to witnesses then the employer knows about it. Or, as with the OP, if they turn their ideas into code, that’s even more revealing.

@DaleM "If they say it out load to witnesses then the employer knows about it". That does not mean that they become trade secret of a company which no longer employs the OP. The OP's post-employment ideas of improvement are not within scope of the agreement(s) pursuant to his former employment. The purpose of laws on trade secrets is to prevent the misappropriation of intellectual/commercial property, not to seize anything and everything that former employees create during the rest of their lives.

@IñakiViggers I never said they were nor are all ideas trade secrets

@DaleM "I never said they were nor are all ideas trade secrets". This whole chain ensued because you yourself stated: "every idea you have about what to write is their trade secret even if you never write it down".

@IñakiViggers read the whole sentence, in the context of a journalist paid to write articles, every idea for an article is potential a trade secret. If they have an idea to use blue paper instead of pink, that isn’t.

@DaleM Again, that does not fit the legal definition of trade secret. The OP's post-employment ideas which supersede the technology his former employer uses are not something that was confided to the OP, nor are they something that the former employer used or knew so as to qualify as "trade secret". In your example you might be thinking of breach of contract, conversion, or alike, but also those theories are inapposite bc the OP came up with the new ideas purportedly after his employment there had ended.