Connection to server mail.optusnet.com.au timed out.

After Thunderbird update 115.12.2(20240621154414) was installed on my PC on the 25/6/2024 I am unable to receive emails. I continue to get an error message on account noeljc@optusnet.com.au (IMAP) Connection to server mail.optusnet.com.au timed out. or Failed to connect to server mail.optusnet.com.au. I have looked thru all the forums and tried various solutions without success including extending the setting for mailnews.tcptimeout to 3000. I have checked and validated my account server settings are as recommended by my ISP(Optus) are correct for authenticated emails. I even turned off my Norton VPN completely to no avail even though I use Split tunnelling to allow Thunderbird thru it as an exclusion. It appears to me there maybe a bug in the last Thunderbird update causing this. I have had this issue in the past at various times intermittently but it has always seemed to correct itself. I have been in contact with my ISP(Optus) regarding this error and all they could say was to logon to email server via webmail and did not offer any other solution. It appears there is a communication breakdown between my PC and the Email server somewhere. As I stated this only happened after the last Thunderbird update on my PC on 25/6 as it was working up until 24/6. I also have another optus email account for my wife on Thunderbird which has the same error messages. Could the Mozilla gurus please advise what to do.