Gmail - Save all incoming and outgoing email to All Mail folder (even deleted items)

I've been using Gmail for years. Up until recently, not sure exactly when, all emails that were ever sent or received were stored in my "All Mail" folder. I loved it. I never had to categorise or tag an email, i could just search and find it! If i deleted an email from my inbox, a copy still existed in the All Mail folder which i could search.

However, i noticed that recently things have somehow changed and if i delete an email from my inbox it also deletes the email from my All Mail folder. Very upsetting as i've now lost a few weeks worth of incoming emails. The sent items are still there, but i that's because they're also stored in the "sent mail" folder and if i delete them from the Sent Mail folder then they are also removed from All Mail.

To test if it was my settings on my gmail account that i broke or anything to do with my computer or devices i setup a brand new gmail account and sent an email to and from it, deleted them and they both deleted from the All Mail folder. So, it seems to me that it's something that gmail have changed on their end.

Very simply, regardless of why it's not working anymore, i want ALL emails to be saved in All Mail, regardless of whether i delete it from my inbox or any other folder.

I need this to work no matter where i access my email (gmail online, Apple computer, iPhone, iPad etc) and no matter where i delete the email (again, regardless of device).

I'll need you to show me or talk me through what settings were changed or rules were created once it's setup too as i have multiple accounts that i want to set this up on.

Thanks,

Chris