Network disconnects in every 15 seconds.

I'm using also W10 and W11 but W7 still remains my favourite.
1. July 2025 there started weird W7 internet interruptions of my desktop Gigabyte GA-B150M-D3H mobo. In Event viewer there were several DNS errors and at first I considered a malware attempting to change DNS servers but I couldn't find any evidences.
As temp remedy I disabled network adapter and instantly enabled again and after that Internet connection was stable next 10-30 minutes.
But finally I disconnected this PC from LAN leaving for local tasks.
2. 4 weeks later my wife's 8 years old HP desktop running w10 started same game. After few days I switched from internal LAN to USB-LAN and so far 3 month no problems with this PC Internet.
3. Now I'm attempting to set up fresh W7Sp1 installation on old Dell Latitude E7440 laptop. And same behaviour. Installed Chrome and later Opera browser but network is periodically disconnecting.

When checking Event viewer - e1 dexpress – I218LM -Network link is disconnected periodically. This event occurs after every 15 seconds.

12:38, 12:53, 13:07, 13:21, 13:35, 13:47

When I installed Dell Latitude E7440 Wireless drivers, Internet connection is stable.
So it appears to be Intel network hardware related issue which appears after some update or something.

Still I couldn't find with Google any more info how to fix.
Somehow it feels that drivers meeting contemporary world just fail because of missing support.
Any ideas?