Hello. My father and I are trying to play against each other. We are in the same room, connected to the same Wi-fi, he is on the laptop and I'm using the PC. Our game crashes almost immediately and it says that we are "out of sync". Does anyone have a solution to our problem?

You must use a different NAT-T port. For example your PC uses 27000 UDP and your father's PC 2900 UDP. Then create two new port forwarding rules, point them to the right PC and don't forget to change the NAT-T port in your Voobly settings.

I found a temporary solution by using VPN on my PC. I tried with port forwarding, an experienced friend helped, but we couldn't resolve the issue. I'm sending you a ss of my routers port forwarding page, so maybe you can tell me what should be put in there.
I found my local IP in command prompt, used 16000 as my port and 16001 as my fathers; for an external IP I left it at 0.0.0.0. I used both TCP and UDP. If you know where I made a mistake, please let me know.

First, change the NAT-T port in your Voobly settings. For Computer A, choose 27000 and for computer B choose 29000.
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Second, you need the local ip address for Computer A and Computer B. Start > Run > type "cmd > hit Enter > type "ipconfig" into Command Prompt. The IPv4 address starts with 192.168.***.*** for usual.

Last step, create two port forwarding rules in your router:

Computer A
Local IP Address: the local IPv4 of Computer A
Local Start Port: 27000
Local End Port: 27000
External IP: 0.0.0.0
External Start Port: 27000
External End Port: 27000
Protocol: UDP
Description: Voobly Computer A
Enabled: On

Computer B
Local IP Address: the local IPv4 of Computer B
Local Start Port: 29000
Local End Port: 29000
External IP: 0.0.0.0
External Start Port: 29000
External End Port: 29000
Protocol: UDP
Description: Voobly Computer B
Enabled: On

And don't forget to delete existing port forwarding rules you already created for Voobly.
Please provide a screenshot of the two newly created port forwarding rules when you are done.