***
If you're not sure this is actually a bug, instead post about it at https://discuss.kde.org

If you're reporting a crash, attach a backtrace with debug symbols; see https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports

Please remove this comment after reading and before submitting - thanks!
***

SUMMARY

id everything AI Overview was suggesting with no results:

There are several potential reasons why a Kubuntu 20.04 machine cannot see a Kubuntu 24.04 machine in Dolphin, most of which relate to changes in network protocols and security settings between the two versions
. 
Key changes and solutions
1. Newer Samba versions and SMB1 protocol deprecation
The older Kubuntu 20.04 client may be attempting to use the outdated and insecure SMBv1 protocol for network discovery, which is likely disabled by default on the newer Kubuntu 24.04 system.
Solution: Enable SMBv1 on the 24.04 machine (not recommended)
This is a security risk and should only be used as a temporary fix or for testing. You would need to add server min protocol = NT1 to the [global] section of /etc/samba/smb.conf on the 24.04 machine. 
Solution: Directly connect using the IP address
The most reliable method is to manually connect using the 24.04 machine's IP address.

    On your Kubuntu 20.04 machine, open Dolphin.
    In the address bar, type smb://<IP_address_of_24.04_machine> and press Enter.
    You will be prompted to enter a username and password for the shared resource. 

2. Firewall configuration changes
Ubuntu 24.04 and its derivatives now use nftables with firewalld by default instead of iptables. The default firewall settings on the 24.04 machine may be blocking the necessary Samba ports. 
Solution: Open the Samba ports on the 24.04 machine
From a terminal on the Kubuntu 24.04 machine, run the following commands to allow Samba traffic through the firewall:

    $ sudo firewall-cmd --permanent --add-service=samba
    $ sudo firewall-cmd --reload
    If this does not work, you can temporarily disable the firewall to test: $ sudo systemctl stop firewalld. If the connection succeeds, you will know it is a firewall issue. 

3. Name resolution differences
Older versions of Linux and Samba sometimes have issues with name resolution on the network.
Solution: Use Avahi and mDNS for name resolution
Ensure the libnss-mdns package is installed on the Kubuntu 20.04 machine for multicast DNS (mDNS) support.

    Open a terminal on your 20.04 machine.
    Install Avahi and mDNS: $ sudo apt install avahi-daemon libnss-mdns
    After installation, reboot the machine or restart the service with $ sudo systemctl restart avahi-daemon. 

You may also need to do this on the 24.04 machine to help with service discovery.
Solution: Add an entry to the hosts file
On your Kubuntu 20.04 machine, edit the /etc/hosts file to manually associate the 24.04 machine's hostname with its IP address.

    Open the file with elevated privileges: $ sudo nano /etc/hosts
    Add a line at the bottom in the format <IP_address> <hostname>. For example: 192.168.1.50 kubuntu24.
    Save the file and exit. You should now be able to connect using smb://kubuntu24. 

4. KIO-Fuse package
Sometimes, the older KIO subsystem in Kubuntu 20.04 can struggle to properly handle SMB URLs from newer systems.
Solution: Install kio-fuse on the Kubuntu 20.04 machine
Install kio-fuse to enable transparent mounting of remote filesystems like SMB shares. 

    $ sudo apt update
    $ sudo apt install kio-fuse
    Restart Dolphin or your machine for the changes to take effect. 

Checklist summary
To diagnose and solve the problem, go through these steps in order:

    Try connecting by IP address. If this works, the issue is with name resolution.
    Check the firewall. Temporarily disable the firewall on the 24.04 machine to see if it fixes the problem.
    Set up name resolution. Install avahi-daemon and libnss-mdns on both machines.
    Try forcing the protocol. Manually specify server min protocol = SMB2 in the /etc/samba/smb.conf on the 24.04 system.
    Consider other tools. If the issue persists, try accessing the share using smbclient from the terminal on the 20.04 machine to rule out Dolphin-specific issues. 
    
    Dolphin is saying:
    
    Internal Error
Please send a full bug report at https://bugs.kde.org
libsmbclient reported an error, but did not specify what the problem is. This might indicate a severe problem with your network - but also might indicate a problem with libsmbclient.
If you want to help us, please provide a tcpdump of the network interface while you try to browse (be aware that it might contain private data, so do not post it if you are unsure about that - you can send it privately to the developers if they ask for it)

   Thunar is saying:
   
    Failed to open directory
    
    Krusader is saying:
    
    same thing as Dolphin

STEPS TO REPRODUCE
1. start dolphin
2. type smb://<ip-address> 
3. select home
4. select <user name>

OBSERVED RESULT

<ip-address> of Kubuntu 24.04 machine is found
for example etc is found
home is found
<usere name> is NOT found

EXPECTED RESULT
 view the same thing as smbclient -L <ip-address>

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: yes
KDE Plasma Version:  5.18.8
KDE Frameworks Version: 5.68
Qt Version: 5.12.8

ADDITIONAL INFORMATION

Kubuntu 20.04 machine is 20.04.6 5.15.0-139-generic
Kubuntu 24.04 machine is 24.04.3 6.8.0-79-generic