Why is my network messed up after update to windows 11 24H2

There is some good advice here, some of which I used to solve my same problem of update screwing my home network. It's amazing to me that Msft makes an update that CHANGES settings functioning fine. I had to do a few more similar fixes to yours to set me back up fine. Both with 2 Win 11 and 2 Win 10 machines on the same network.

Well, to start 2 of my machines running 24H2 meet all the requirements set by Microsoft. 1 laptop of 2018 which nearly meet all the requirement (missed on the processor, an i5 gen.7). That's quite an history. A Dell inspiron 15, from my wife, who I gave a new Asus. So, retting it to manufacturer settings, it installed 22H2 instead and then told me it was not compatible for Win11. Didn't use any extra tools, just a registry key change. That being said, I do use "users & passwords" because I sometimes have people staying over and using my guest-network and guest-computer. I do not want them accessing any of my resources, but solely provide them internet.
I also do not use the trick to install every time the latest downloaded version of 24H2. That would indeed reset some things concerning networks.
I only do regular updates.
Some of my findings are already in former replies in this chat.
So:

1. using a Synology NAS, already had users & passwords. Had to add "server signing" on on the NAS.
2. In the network connection of the Windows 11 machine, you have to enable NETBIOS (Yes, 24H2 disables this)
   Control panel > Network and internet > Network connections
   select network protocol version 4 (TCP/Ipv4) and click properties
   go to the WINS tab and enable Netbios over TCP/IP
   click Ok till you exit the network connection. Now, restart the PC.
3. GPEdit.msc (Group policy editor)
   Change Computer configuration - Windows Settings - Local Policies - Security Option the settting Network security: Restrict NTLM outgoing: allow all4. Check your network adapter (WiFi or wired) is set as "local network, NOT "public" and check in "advanced sharing settings" to put "file and printer sharing" to "on". If your network is still on "public" it will restrict the connections.
4. the firewall could be blocking connections. Type "defender" in search. Open "Windows Defender Firewall with advanced security" and check inbound rules as well as outbound rules if "file and printer sharing" is checked (green).
   

It's quite a bit. And even if it all worked with 23H2, 24H2 does mess up, sorry, does make it more secure.
I hoped it would all work when you migrate from a working PC on Win10 or Win11 23H2 to 24H2.

Now, I update my Win11 pc's without further problems with my network. And the more resent versions of 24H2 are better than the first ones.

I hope this information does help you solve your network troubles with 24H2.

Thank you for your comment. If you figure it out, please post it, because other people are having the same problem. Still I am sticking with Windows 11 for many reasons. Nonetheless, after having so many issues with networking (as are thousands of other users), I was tempted to experiment with other OSs. I really like Synology NAS, but now they are requiring that users utilize "approved" storage device brands, which I think is abusive. My favorite NAS now is TrueNas because of the ease of use, but Open Media Vault is simpler and has interesting apps (which Truenas Scale no longer has). I have used Windows 11 24H2 on 13 year old machines without a hitch, but none accepts connections from other computers without a user password. Even when we choose to share with "everyone" on the network sharing settings. I heard it is a security issue, and I will accept it for lack of a plausible explanation. Up to Win11 23H2, everything ran as smooth as can be.

Kubuntu (KDE Ubuntu) runs all the applications Windows does in their Linux versions and is compatible with all Windows hardware I have used so far, even wireless internet dongles and cards. Bluetooth also works like a charm. When using it, I cannot tell the difference, except that it does not require new hardware. One of my Kubuntus is running on an AMD FX8, 16 GB RAM and a stupid 2GB NVidia video card I plucked from an old computer I picked up from the garbage, and an the other runs on an i5 3rd gen Dell 990 SFF. The HDMI works beautifully on both. Networking works very well on SMB protocol, but it is slow.

I am wondering why the SMB protocol is deinstalled with every update at your machines.
I migrated from Windows 10 to 11, had 24H2 installed afterwarts. No straight upgrade of the network, as I hoped. But after putting the protocols correct, I do not have to correct them again with every update of the 24H2.
In my network runs a Synology NAS, some Windows 11 machines and some Windows 10 and 1 Ubuntu. The Windows 10's and the Ubuntu are older machines not compatible with Win11 at all.
I made some shares on the Windows 10 machines as for some reason I need to copy files to them. No problem with the shares on the Synology nor the Win10 machines.
So, I'm wondering what triggers Win11 to remove every time the SMB protocols on some machines and not on another.

Though I agree with the monopoly part, I need to say there is nothing out there with the same level of compatibility with current software. Apple is guilty of the same sin you denounced. However, the current situation has opened my mind to other avenues: I created two NAS file servers, one with Truenas scale and another with OpenMediaVault. I noticed that both work flawlessly with SMB protocol - even better than Sinology NAS. I am testing both and will stick with one. As for inter-connectivity between the network, I caved in and created passwords for every computer on the home network and enabled password required when accessing them option. I also created a Windows 11 file server which is super fast. The caviats with NAS is that if the system breaks, you cannot easily recover the files from their hard-drives. An easier solution is to use 2 storage HDD on each NAS. Another way is to make one replicate itself on another NAS. Neither is a "little-hardware" solution, but all will do the trick. I still don't understand why every update to Windows 11 24H2 uninstalls the SMB protocol, making you go back to control panel and re-install them. What is the purpose in doing it? We'll find out some day with Windows 12. I also created a Kubuntu machine for testing. It works like a charm, but slow.