There are pcb manufacturers offering special high current pcbs. It is possible to reinforce only the traces used for high currents. The pcb has normal traces with 35 µm copper and the usual trace widths of 0.2 mm to 0.5 mm or more for low currents as well as high current traces with 200 µm or more copper and widths of 5 mm or more.
About 10 years ago I made such pcbs working for an university. The pcbs were plated two times, the first time to build the 35 µm traces, after etching a second time to reinforce only the high current to 200 µm.
The current for galvanic reinforcement of the traces was connect to the edges of the pcb. Only those traces connected to an edge were reinforced, the other traces without a connection to an edge got no additional copper.
Here is an example with 350 ; 700 and 1050 µm traces.