Your port looks as closed/firewalled, you are passive peer?
When having OpenVPN server, one can setup it to route the traffic properly to OpenVPN client and that way OPEN the port/s.

On the server,
Enable IP forwarding in /etc/sysctl.conf on server: net.ipv4.ip_forward=1
Execute following for the changes to take effect: sysctl -p

iptables rules to be executed on the server to opening its port - forward incoming traffic to the tunnel:
iptables -t nat -A POSTROUTING -o venet0 -j MASQUERADE
iptables -t nat -A PREROUTING -i venet0 -p tcp --dport 1234 -j DNAT --to

Before executing, read following and adjust above commands.
1234 - port to open, properly forward its connections into the tunnel. Range can be defined like this: --dport 1234:1240 and the "--to" would miss the port and only IP possibly. - local IP address of the OpenVPN client network interface/adapter (shown by the OpenVPN client software and also in "ipconfig" Windows command output; it can be different like
venet0 - Linux server network interface name (usually one with most traffic reported by "ifconfig" command, often "eth0")
tcp - connection type. there is also for example "udp", it may be needed to add one more rule separately for udp if is needed

If added wrong rule, you may delete rule for example: iptables -t nat -D POSTROUTING RuleNumber (number discovered by command "service iptables status")

On the OpenVPN client, add new firewall rule that says something like:
Allow INcoming connections to port 1234 and place the rule somewhere on the top of the list as top rules usually has higher priority.
You may check the open port:

If it is closed, then try disabling firewall (not ideal) to see if the firewall causing the block.

If port was opened successfully, then save server iptables rules, so it is not lost on reboot: service iptables save
Some servers does not use iptables, but firewalld for example, so the command would be different.
Possibly edit resulting iptables file to keep only wanted rules. Note that OpenVPN and Wir€guard automatically insert its default rules to iptables when starting, so you may remove these from the file. After reboot, you will see if there are any duplicates (iptables -S).