DIAGNOSIS Your device (like a phone) is probably connecting to the 2.4 GHz band for a more stable signal, which is much slower, instead of the faster 5 GHz or 6 GHz bands. The router's "Smart Connect" feature might be making a poor choice for your location.
FIX First, run a speed test right next to the main router node. If it's fast there, it's a coverage issue. If it's slow even there, let's check the band. In the Linksys app, go to Wi-Fi Settings and look for "Smart Connect." Turn it OFF. This will split your network into separate SSIDs for 2.4 GHz, 5 GHz, and 6 GHz (you'll see names like YourNetwork-2.4G and YourNetwork-5G). Connect your phone specifically to the network that ends in "-5G" or "-6G" and test your speed again. You'll likely see a big jump.
IF THAT DIDN'T WORK There might be channel congestion. In the app, under Wi-Fi Settings, look for "Channel Finder" or a similar tool. Run it. It will scan the area and pick the least crowded channels for each band, which can significantly improve performance, especially on 5 GHz.
HEADS UP The 6 GHz band (Wi-Fi 6E) is the fastest but has the shortest range and won't go through walls as well. For best speeds, you need to be in the same room or have a clear line of sight to a node. For general use around the house, the 5 GHz band is often the best balance of speed and range.