om my laptop, using leap 15.4 and KDE Argon, sometimes I use it from afar so I need bigger fonts and also bigger icons when I use it from close, I thought that doing different use in different activities ( I thought that activities was done for this type of use) could solve bu seems not, every time I have to go to >systemsettings>appearence>fonts and change font size becouse font size is for the whole system, is there a way to have some sort of profiles to switch among them when one want to change appearence of desktop??
Different user accounts perhaps?
Depends what “from afar” means. If you mean a smaller display or sitting farther from the display, there might be a way. Logical display DPI constitutes a scaler. DEs use logical DPI for that purpose. In Plasma, DPI can be changed to a limited extent on its fonts setting screen. Behind the scenes, Plasma changes DPI via xrandr, thus xrandr can be used directly for scaling, but it only affects what’s newly started after a change. That means the DE needs to be restarted before you can enjoy the full effect of the change. If xrandr is employed globally, it will affect any DE or WM you start. For global effect, I place an xrandr mini-script in /etc/X11/xinit/xinitrc.d/. e.g. xrandr --dpi 132. Alternatively, DisplaySize can be used in a /etc/X11/xorg.con* file. This requires a bit of math, and an X restart, but an example would be /etc/X11/xorg.conf.d/50-monitor.conf containing:
Section "Monitor"
Identifier "DefaultMonitor"
DisplaySize 369 208 # 132 DPI @ 1920x1080
EndSection
This translates physically to a screen size of about 16.5" diagonal, but logically scales most objects bigger when applied to screens larger than 16.5". 369 & 208 are millimeters. # 132 DPI @ 1920x1080 is a mere comment (not necessary). This scaling method is employed sooner than xrandr can be, and affects the login greeter screen, while xrandr is only applied after logging in. If you wish to use xrandr directly, or DisplaySize, then in Plasma font settings DPI should be left unset.
it works, but quite more complex intead of a single click switching activities 
manythanks but I’m looking for a single click solution, is less complicate to switch fonts size in system settings than your solution
That’s a first world problem. Switching user is not hard. 
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Nope. That’s not what activities are for…
https://docs.kde.org/trunk5/en/plasma-desktop/plasma-desktop/activities-interface.html
https://docs.kde.org/trunk5/en/plasma-desktop/kcontrol/kcmactivities/index.html
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Just in case this thread is of interest to you
I tried to set a blank password for another user account but it seems not possible, is there a way to have a blank password user account??
I tried automatic login but it automatically login for that user-with-big-fonts and I don’t want this
interesting, I could use another file and web browser than dolphin and chrome and set its fonts bigger, I will try
If it is only browser application use you are interested in, then you can scale individual tabs quite simply. (I do that when viewing certain sites with firefox.)
right, it says “Activities are a way to have multiple Plasma™ setups, with each a different set of widgets and themes” and I supposed that fonts size was a plasma setup non system wide setup, I will file this as a wished feature in kde maybe
It isn’t system-wide, it is per user. 
yes for web browser I know, for dolphin I have to use systemsettings I suppose
yes, right, per user
sudo passwd -d username
man passwd
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Converting the invocation of an application into a single click action is straightforward:
[Desktop Entry]
Comment[en_GB]=
Comment=
Comment[de_DE]=
Exec=/usr/bin/systemctl start dup.service
GenericName[en_GB]=
GenericName=
GenericName[de_DE]=
Icon=system-upgrade
MimeType=
Name[en_GB]=Dist-Upgrade
Name=Dist-Upgrade
Name[de_DE]=Dist-Upgrade
Path=
StartupNotify=true
Terminal=false
TerminalOptions=
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=
X-KDE-SubstituteUID=false
X-KDE-Username=
Basically you need to fill in the invocation Exec=... into the template opened with “Desktop Background > Create New > Link to Application”.
Is not font a part of theme? If it is possible to configure different themes, I expect it should be possible to select different theme with different font?
And what is "it’ about? There are a lot of posts before yours and it is absolutely unclear which one you answer.
It was a reply to this post