Error code: 1609891835 - Premiere Pro could not start audio plaback.

In January, I started editing a project on a 2017 iMac, 2TB internal HDD with about 130GB free, using Premiere Pro v25.6 and proxies. It had to be sent serviced at an official Apple Store, for an internal cleanup as the fan started making a noise. Chose to upgrade the internal drive from a 2TB HDD to 2TB SSD, details of which I have shared in screenshots below.
Meanwhile, I resumed my edit on a rented Macbook Air M1, 2020 (8GB). Mid-project Premiere Pro auto-upgraded from v25.6 to v26 and I continued editing till 2 days ago. The rental period lapsed and I had to return the Macbook Air and resume working on the serviced and upgarded iMac.
The first problem I encountered was that the iMac isn’t compatible with Adobe app v26 so I installed v25.6, which didn’t allow me to open my project files as it was created in a newer version. I first used https://downgrader.elements.tv/ to downgrade the project, but v25.6 couldn’t open that file saying the file may be damaged. After following some instructions provided by Jamie Clarke - Community Manager on a similar thread on the forum, I installed the more stable v25.5 and deleted all media cache files. Using the above premiere pro downgrader, I downgraded the project file again and was able to open the project file on v25.5.
Then arose the second problem. All my footage timelines and line-ups that were made before premiere pro auto-upgraded in the Macbook Air are playing back properly, both video and audio. However, the newer edit timelines and selects timelines are not playing or allowing my to playback and/or edit. Meaning I am able to scrub, move frame by frame, copy-paste, insert-overwrite onto the timelines but have been unable to edit. It shows me the YELLOW ERROR CODE: 1609891835 - Premiere Pro could not start audio plaback. I went through the Community Forum again, deleted media cache files from Premiere Pro as well as the ~Library/Cache, reallocated the media cache location from my external edit drive to the internal SSD, etc. None of that worked. I was simply unable to playback. Then on another thread someone mentioned that I should select Adobe SRT in the Playback preferences. This allowed the playback of the video but audio is still not playing and I continue to get the error message as mentioned in the subject. I tried out different codecs in the Sequence Settings - Apple Prores Proxy, LT, H.264, etc. None of these steps have solved my problem.
Lastly, I came across a forum thread where someone mentioned installing the MacOS on the same internal SSD. I am unsure whether the service centre personnel installed the OS on a separate partition, therefore have shared screenshots of the Dis Utility specs as well.
I have shared all the relevant screenshots that another forum had suggested uploading. Older HDD, Upgraded SSD, external drives, system specs, project settings and sequence settings. Is there anything else required in order to find a solution to this problem? Please help!