Adding some further detail to Gene2memE response. There is a lot of nonsense talked about 5G, so it is good to see a sensible reply. 5G is not some secrete means to kill the US population and has nothing to do with Covid or vaccinations. The technical standards are all publicly available on the 3GPP website, if you have a spare year or ten to read them.
5G offers significantly greater numbers of connections in a given area (~1000 times more), about 1/10th the latency and about 20 times the connection speed, along with substantially smaller connection bases (no more need for large cell towers).
With a 5G connection, I can stream 1440p video with no issues on my phone or laptop. If I turn that off and rely only on 4G, I can just run 720p on the same device.
5G uses essentially the same RF transmission schemes (modulation) as 4G/LTE but can support up to 100MHz channel bandwidths, while standard LTE/4G supports up to 'only' 20MHz bandwidths. It is this increased bandwidth that allows the much faster speeds.
4G stands for 4th generation, which is also called LTE (Long Term Evolution).
5G is 5th generation (not to be confused with 5GHz band used for WiFi)
4G and 5G operate on different frequency ranges and across different bandwidths within those ranges. If you buy yourself an RF microwave detector (~$500 to $800 for a good one), you can detect which frequencies are operating in your area.
5G has added some new frequency bands, principally in the 3 - 5GHz spectrum. Band n77 (3300 - 4200 MHz TDD) seems to be one of the more common bands. There is much more spectrum available here, so there is the space to support much wider channel bandwidths and thus give the higher data speeds people want.
However all the existing 3G and 4G bands can be repurposed for 5G. The network operators will want to turn off their 3G networks and repurpose those channels to 5G. It will take much longer to do the same with their 4G channels. I expect that the existing bands will be used for both 4G and 5G for some years.
You will not be able to tell the difference between a 4G and a 5G signal, except if the signal bandwidth is too wide for it to be 4G. But LTE-Advanced also supports carrier aggregation giving up to 100MHz bandwith (with the right test equipment it should be possible to tell the difference).
In principal it is possible to detect the difference between 4G and 5G signals in the 'up link' i.e. transmissions from the handset. But probably not with any test equipment you could afford to buy.
Yes, an RF analyser will show you what signals are being transmitted but is unlikely to identify whether they are 4G or 5G.
5G uses a pair (or even three) bands. Exact frequencies depend on the country, but the base band is similar in cabilities to 4G (known as the 'low band' or 'Sub-6' band, generally in the 400 Mhz to 7 GHz range). In addition, there is the 'high band' which operates on the much higher millimetre wave frequencies in the 25-54 GHz range.
Some countries also use a mid band in the 3 to 24 GHz. Where I live, for instance, there is a band in the 2.5 to 3.8 GHz range. This adds about 25% to overall system capacity.
4G also suports carrier aggregation. I think 5G takes it even further.
Besides all the useful bands in what 5G calls FR1 (410 MHz – 7125 MHz), there is the new FR2 also called mmWave (24250 MHz – 71000 MHz ). These offer even wider bandwiths up to 400MHz (and hence faster speeds). But the main problem is these signals have very limited coverage as they are very easily blocked, so I don't see how they are useful unless you have the basestation attenna in the same room.
