For anyone reading or watching ads and articles you are going to be bombarded with terms that can be very confusing. Simply put, the "G" here is the generation. Advances in technology happen in steps and when there is a major leap forward it is often defined as a new generation. To further complicate this, there are multiple technologies that are defined in Generations, and they do not have any connection to each other. The top two technologies that are pushing generations right now are Cell Phones and WiFi Routers.
In the world of cellular technology the one still used by most of us is 4G LTE and the newest one being pushed in most of the ads is 5G. While bigger, better, faster is always a good thing, it may not always be necessary. If you have a good 4G signal on your wireless device, you would be hard pressed to notice any slow down. The newest technology in wireless is 5G and it dominates most of the ads and the wireless companies are pushing it hard, but unless you have a newer device that has the ability to use 5G, you are still using 4G. My iPhone XR is a 4G phone and only the iPhone 12 has the ability to use 5G. My XR phone still works just fine and I have not felt the need to upgrade yet, but when the time comes for an upgrade I will want 5G.
In the world of WiFi Routers there are many standards still in play but the latest and greatest is WiFi 6(G), and more specifically 6(G)E. In the past WiFi standards were not defined by generation but using the 802.11** designation. Fortunately, with each new generation of WiFi standards, they have maintained backward compatibility so your older devices will still work. The WiFi starndard used by a device is not always clear but that has never been an issue thanks to the backward compatibility. What do you need? That is hard to answer clearly because for most of us older generations are more than enough. Unless you have a clearly identified need for the latest WiFi6 standard, you don't need to stress over that decision. It is always advisable to get the newest and to buy the best that you can afford but it is not critical in this case. I am still using Apple Airport wireless routers and Apple exited that space several years ago now. The WiFi signal in my house is much slower and less capable than the latest WiFi6 devices would support but things still work. In fact, you need to have newer devices to even use the latest standards. My older MacBook Pro from 2012 used older WiFi standards so there would not have been any benefit to getting a newer router, but now that I have new MacBook Pro with WiFi6 there is reason for me to consider upgrading. My motivation is not so much for the extra speed but mostly because my hardware is older and on occasion is starting to be a bit flaky. I will expect any new routers to last for many years so buying the newest technology is the best way to insure they can last. Speed is not the only improvement for sure, newer routers have other features and stronger signals that can eliminate dead zones and many use mesh technology to better cover larger homes.
Most of the time when things slow down the reason is too much demand on the network. Cell networks and Cable based Internet are shared bandwidth systems, there is a total capacity that is shared with all the users, like slices of a pie. The more users the smaller your slice and anyone who has attended a big event has seen what happens when the network is overloaded. One of the major advances with 5G Cell Networks is the "pie" is much bigger so it will take many more users to slow it down. They claim the pie is big enough to support home internet solutions based on the cell network. The major carriers have all announced home network solutions but none are here in Sun Lakes yet. Likewise, with cable internet, there are times of the day where service tends to slow down and this is why cable providers always spec speed as "up to xxMB/sec". Connection to the internet is much like a chain with many links between you and what you are looking for and just like a chain, the speed will be limited by the slowest link in that chain. It is frustrating when you need to wait or see the buffering symbol but it is hard to know for sure what link is causing the delays.
Lastly there is nothing out there yet with 7G but it will be here before we know it.