Thank you kindly for letting us know you solved the problem, and how.
Re: "so far I am yet to figure out how to connect my left hearing aid at all" ...
Wondering if the volume could be set so low it appears it is not connected ...
Try checking in Settings > Accessibility > Audio/Visual > Balance, and make sure the balance is set in the middle.
About Hearing Aid Compatibility (HAC) requirements for iPhone - Apple Support
says:
"If you already own an iPhone and a hearing aid, here are some tips to ensure that you have the best experience possible.
iPhone and hearing aids generally work best together in "M" or Acoustic Coupling mode. To use your hearing aid in this mode, make sure that your hearing aid is set to "M", or Acoustic Coupling mode, and position the iPhone receiver near the hearing aid’s built-in microphone (or microphones). In other words, hold your iPhone against your head as you would naturally hold the phone when making a telephone call. The hearing aid will receive audio from the iPhone through its built-in microphones. For the best results, try using the iPhone in different positions relative to your hearing aid — for example, placing the receiver slightly above the ear may result in better performance for hearing aids with microphones positioned behind the ear.
If Acoustic Coupling does not produce a satisfactory result, try using your hearing aid in "T", or telecoil coupling mode. To use your hearing aid in this mode, make sure that your hearing aid is set to "T", or telecoil coupling mode (not all hearing aids have this mode). If you have an iPhone 5 or later, activate Hearing Aid Compatibility (see below).
________________________________
Activate Hearing Aid Compatibility
To activate Hearing Aid Compatibility on an iPhone with iOS 13 or later, go to Settings > Accessibility > Hearing Devices. On these iPhone models, Hearing Aid Compatibility modifies the phone’s acoustic settings to improve compatibility with hearing aids set in "T" or telecoil mode."