First, welcome on this forum.
Next. KiCad’s version numbers have 3 digits and two dots. This is a quite important distinction. Increments in the third number are bug fix releases, and you should always update to the latest bugfix release. Currently it is V7.0.10 and after V7.0.6 likely around 300 bugs have been fixed.
About your highlighting issue…
I have no idea why you tried: Alt + N or Alt + M. KiCad has several highlighting options, and those key combinations are not used as hotkeys in the default configuration.
The simplest highlighting function is with the backtick key (left of the 1 key on an US keyboard).
For other Highliting hotkeys you can go to … / Preferences / Preferences / Hotkeys and then start typing the first few letters of whatever you want to know more about in the search box. In this case Highl. This narrows down the long list to your items of interest.
I do not have any problem finding higlighting funtions. Mine is Alt + N for a reason deault.
My problem is: when I higlight a single track/net, the whole card is higlighted.
All or nothing.
That`s my problem.
It’s a guess, but maybe you are confusing “Highlight” with PCB Editor / View / Contrast Mode / Inactive Layer View Mode.
Maybe something unusual happened with your configuration. You can try to:
Exit KiCad.
Rename KiCad’s configuration directory.
Start KiCad again.
This resets all configuration options in KiCad, and KiCad starts as if it is the first time it is ever started from that computer and generates a new configuration with all the defaults.
If that does not help, you can simply delete the newly generated directory and rename the old to it’s default to get all your configuration settings back.