I worked in retail for quite some time. I'm not saying there are no crap retail staff, but my experience, that of friends and just observation when in shops- in most cases, my money's on management being the issue. Customer service staff are now expected to go above and beyond (remember that there is now very often an expectation they do social media marketing stuff for no extra pay.) In my experience and that of many others, there just isn't enough time in the day to get done what employers now ask.

Also the whole "young people are rude" thing is straight-up BS. This is anecdotal but I always found millennials and younger to be unfailingly polite, and understanding if we weren't able to honour a request. The arsehole customers were almost always Boomers, with some Gen X (for disclosure, I am Gen X myself.)

As a customer, I find the same. Young customer service people are usually lovely.

Try not to blame the person you're actually interacting with. They are seldom the issue.