Scoppy app - thanks to this app for Android phones, you can have a portable oscilloscope and logic analyzer with Raspberry Pi Pico right on your phone. The Raspberry Pi Pico offers great performance and the price of the board itself is very low. How to do it?

And you don't need much, the Raspberry Pi Pico itself, two resistors, a breadboard, a microUSB cable. And then a smartphone and install the Scoppy app. It has a great rating on googleplay - 4.9* and over ten thousand downloads.

And what are the parameters? In oscilloscope mode 500ksps and in logic analyzer mode up to 25Msps.

Instructions for construction can be found at https://how2electronics.com/diy-smartphone-oscilloscope-using-raspberry-pi-pico
The Scoppy app can be downloaded at https://play.google.com/store/apps/details?id=xyz.fhdm.scoppy&hl=en&gl=US&pli=1

If you appreciate Wi-Fi connection to your phone instead of microUSB and enabling two channels instead of one, you need to buy the premium version of the Scoppy app (approx. 2USD)

There is also a partially assembled PCB where you need to rewire the BNC connectors and other small things. I contacted laskakit.cz to see if they would like to resell the PCB here in CR/SR.
https://store.fhdm.xyz/fscope-500k
Alternatively, a fully assembled https://store.fhdm.xyz/dso-500k
Thank you for the tip Jiří Dobrý