connection to thunderbird server timed out

Question

I have 13 Gb of mailbox full. There are many photos as attachments that I have in my email box which I suspect have taken most of the space.

I configured Thunderbird on my Ubuntu virtual machine and tried to download all emails but since 13 Gb is too much to download obviously it created problems. So, someone suggested me to register for google takeout and download the data in mbox format. I tried doing that. I have a bit slow internet connection and intermittently it keeps disconnecting. So could not fully download it and this resulted in more problems which since Google allows only 2-3 times once it created an archive of data to download. In my kind of internet connection (which is slow), I exhausted my attempt limit to download my email data. I get a message mentioning I exceeded download limit

Now I switched to another method.I installed Thunderbird in Ubuntu 19.10 in Vmware workstation. I tried configuring it to use with Gmail. But I get connection timed out problem.

How can I get rid of this problem while downloading and download all the 13 gb emails with all attachments under these conditions? Or is there a better solution for this problem which I am not aware of?

I first want to take a backup of the emails then delete them one by one going through all of them. I have 3-4 days back deleted 675,555 emails as per my understanding I deleted them from Thunderbird interface don't know if they are actually deleted from Gmail also or not. There are thousands of them which I am yet to check. I probably have deleted more than required mails and now I am finding difficult to sort them out and go through them. I read a question here and in the last reply, on above link the original poster mentions that photos from smartphone got synced and that was shown in as Gmail quota limit exceeded. However, I don't have that case as per my understanding because I do not use this account in the best of my senses to have photo backup. Moreover in my email box on this link, it shows me following:

So I think this is problem with my Gmail inbox only.