Coffee bags

They've been around for years in supermarkets, unless I've misunderstood what you mean! Lyons do different strengths. They come in individual sachets, so are handy for holidays etc

Lyons have made them for some time. They are in supermarkets, certainly in Tesco and probably others too. Each coffee bag is sealed into a plastic outer, so they are fresh until that is opened, then they are in a green outer box.
We used to use them in the caravan (a real cup of coffee without any grounds to get rid of) They are strong enough to get a second good cup out of each bag. More recently I took some on holiday in my suitcase, as I never enjoy the little sachets of instant coffee that are provided in the rooms. They took up hardly any space.

They've been around for at least 25 years or longer

I used to take them to work in the 90s!

Unless I'm losing the plot here

They were about twice the size of a teabag and contained ground coffee.

We used to buy brown plastic "cups " with holes in the bottom containing ground coffee covered by porous paper through which boiled water was poured. The container was of course , placed over a mug or cup. This was at least 40 years ago probably nearer 45.

Well I've obviously been living in a bubble
I have seen the 'pods' you describe annsixty but not the bags.