Troubleshoot the addressing
The router is configured correctly: Gi0/0 is 192.168.10.1/24 and Gi0/1 is 192.168.20.1/24. Yet neither PC can reach the other LAN. Find what's wrong in each PC's settings and fix it, without changing the router. Each PC should keep its own address.
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Solution explanation
PC1 had a /16 mask (255.255.0.0), so it believed 192.168.20.10 was in its own network and tried to reach it directly with ARP, which nobody answered: "Destination host unreachable" from its own address. PC2's gateway, 192.168.2.1, isn't in 192.168.20.0/24 at all, so PC2 couldn't send anything off its LAN. With a /24 mask on PC1 and gateway 192.168.20.1 on PC2, both work.
Show solution
[PC1]
ipconfig
ping 192.168.20.10
netsh interface ip set address "Ethernet" static 192.168.10.10 255.255.255.0 192.168.10.1
[PC2]
ipconfig
netsh interface ip set address "Ethernet" static 192.168.20.10 255.255.255.0 192.168.20.1
ping 192.168.10.10