Has anyone here had severe delays (talking months long delays) in receiving/sending mail for the past 4-6 months or so?

I got a Christmas letter 3 weeks ago that was mailed out on Dec. 19th. I just considered it lost back back in January.
I sent a package out back in February that was seemingly stuck/lost(?) at a random post office for 5 weeks before tracking eventually updated on it and arrived 4 days later.
I'm currently waiting on 4 packages (from three different retailers) that have been in limbo at a random post office since March 17th.

Last month, my father had to drive over an hour to a Humana facility to pick up his medical items that either got lost, or are still stuck in "package awaiting acceptance" hell at some post office somewhere.

Yes.

I work in a call center where people send us checks and from Nov-Feb I spent 8 hrs a day telling people about the mail delay.

The pandemic has led to record levels of mail being sent since people are doing less things in person, plus record numbers of mail people out sick with the virus.

Besides maybe one or two instances of mail arriving a day or two late last year, I didn't have any issues sending or receiving all of last year. I, of course, know COVID has impacted mailing and increased delays, it's just pretty sudden regarding me and a few others I know, and it's not just a day or two, or even a week delay, it's become several weeks to months. I suppose I just figured wrong in assuming the bulk of delays would have occurred last year, and not hit a wall like it has in recent weeks/months.

I imagine working a call center right now really sucks, so definitely feel for you there. But you probably have a pretty high tolerance level if you've managed it for a couple months already.

I have worked there since July haha but yes I am very tolerant, you can probably tell that by the fact I stay on this site despite my political beliefs.

Has anyone requested a refund on Amazon after the option has become available? They say it "may still arrive", but I can request a refund now. I've been waiting on this particular package since March 11th. Another package from Amazon will be eligible for refund in two more days too.

What happens to packages if they are still in transit but a long enough time passes for a refund to be issued?

You get it for free because it's a bigger hassle and often more expensive than the product to send packages back.