There's some blatant misinformation going on here. This has nothing to do with the v1 or v2 Speech-to-Text API, and even if that were the case Google has made no mention of retiring the v1 API.
The limitation is that to transcribe audio longer than 60 seconds, the audio must be saved data to a Google Cloud Storage bucket and processed asynchronously. For short audio, 60 seconds or less, local audio files can still be provided and are processed synchronously:
https://cloud.google.com/speech-to-text/docs/sync-recognize. This applies to both the v1 and v2 API:
https://cloud.google.com/speech-to-text/v2/docs/sync-recognize "
Audio content can be sent directly to Speech-to-Text from a local file, or Speech-to-Text can process audio content stored in a Cloud Storage bucket."
So this is down to 3CX choosing to switch all transcribing to the asynchronous api for audio processing, which requires files stored in a Cloud Storage bucket. I would love to know the percentage of voicemails (not recordings) that actually breach the 60 second mark.
I think a lot of the frustration comes from the lack of notification or guidance. In the v20 upgrade checklist page:
https://www.3cx.com/blog/releases/v20-upgrade-checklist-faq/, it is targeted at preparing for v20, not what to do post upgrade. Yet some of the items (Step 2 and 3, regarding departments) are not possible pre-upgrade because Departments is not a feature of v18. And the only mention of Transcription is in the Step 9 FAQ in regards to how long v18 will remain available, but no instruction on steps that will need to be taken for transcription to continue working. 3CX simply broke the feature with no heads up.
The upgrade document should be split into a Pre-Upgrade and Post-Upgrade checklist, with callouts for breaking changes. Here's an example I just dealt where the vendor provided a great checklist document:
https://www.visualsvn.com/support/topic/00233/