How can I improve a very weak 5G router signal through dense forest?

A signal amplifier or repeater may help in some situations, but it is not a solution if there is almost no usable signal outside. Test the signal around your property first, especially at higher points. If the signal is poor everywhere, an amplifier will have very little to work with.

An external cellular antenna is probably the first thing to investigate. If your router has antenna ports, a directional antenna mounted outside and as high as practical could help it receive the tower through the trees. You’ll need to check which bands your provider uses and whether the router supports external antennas.

If the current router cannot connect to an external antenna, consider a cellular modem or 5G router designed for outdoor installation. You could place it on a roof, mast, or other elevated location and run Ethernet back indoors. Some models include directional antennas, while others let you attach one separately.

These upgrades can cost considerably more than a normal home router, especially if you need a weatherproof unit, long Ethernet cable, mounting hardware, or professional installation. If the tower is blocked by terrain or the forest is too dense, a different service such as satellite internet may be more reliable than trying to force a weak 5G connection.