Only 25-47W out of 200W is used on my RTX graphics cards.

Using Lubuntu, I can't find appconfig.xml
It supposed to be in projects folder, but I have no access to it.

What can I do to increase GPU activity?

Cant access unless you are elevated mode ie: "sudo"

What project are you using GPU on ? Some project do not make a lot of use of the GPU.
Some projects, milkyway for example, can have multiple tasks running on the same gpu which "ups" its usage.

SETI has a command argument "-nobs" to force the CPU to dedicate itself to the GPU. That goes into the appconfig.xml and you probably should ask over at SETI for advice

app_config.xml (including the underscore '_') isn't a file made by BOINC, you have to make it yourself. So if it isn't in the project's directory, you make it. Ask at the project of choice what's to be put in it. Then follow the guidelines at https://boinc.berkeley.edu/wiki/Client_configuration#Project-level_configuration

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Cant access unless you are elevated mode ie: "sudo"

What project are you using GPU on ? Some project do not make a lot of use of the GPU.
Some projects, milkyway for example, can have multiple tasks running on the same gpu which "ups" its usage.

SETI has a command argument "-nobs" to force the CPU to dedicate itself to the GPU. That goes into the appconfig.xml and you probably should ask over at SETI for advice

I do what? sudo cd projects?
cd doesn't work under sudo.
I suppose I could do sudo nano /projects/app_config.xml , and then save.
It just feels weird not to be able to see what's inside the folder...

The GUI browser (PCManFM QT manager) also didn't allow me to change security permissions on the folder.

I'm currently running Moo! Wrapper, and Milkyway. I had to disable it in favor of other programs, as the projects used too little resources.
It's going to be a cold night tonight, so I want my servers to run their heaviest stuff tonight!

The GUI browser (PCManFM QT manager) also didn't allow me to change security permissions on the folder.

Strange, I have no problems changing folder and file permissions from thunar the default file manager in xubuntu. after running

sudo thunar

This also lets me see all the boinc folders.

I'll try to SUDO my PcManFM.