Not true. It's 2021 and I am still having the same issue. People saying "oh no this is is a bug issue and it will be fixed in the next upgrade". L I E.
There are a myriad of reasons why a backup may fail that could be related to pgAdmin, PostgreSQL, the database itself, or your system.
Noone has lied about fixing any bugs. If we say they're fixed, then as far as we can reproduce them and test for them, they're fixed. There may be other variants or circumstances that cause an issue that we cannot reproduce, and therefore either don't realise are there or don't get fixed by the same change - it's impossible to test for everything; realistically the thousands of test cases we do run every day can't possibly cover every possible situation.
Accusations like yours are not welcome on these lists and are likely to get you barred from posting. What is welcome is courteous discussion, and constructive feedback to help the developers and other users.