What's is yx8018b and what is it symbol?
Although I can't answer the details about the variations of the YX8018 (with or without a B suffix) it is a solar LED driver, similar to the YX8050 whose output waveform I captured in a previous answer.
The datasheet for the YX8018 shows a sample schematic like this:

The inductor (marked &quot;L&quot; in the schematic), required for the boost converter inside this IC, is what you have misidentified as a 270 MOhm resistor. In fact, it is a 220 µH inductor - that is why it measures as such a low resistance.
This additional photo supplied from comments, shows two of the inductors: The &quot;loose&quot; one on the left side of the photo shows the red, red, brown, silver colour bands more clearly than the one still soldered to the PCB on the right side:

Different inductor values are used to change the LED current, as described in the datasheet's table:


I have no idea what the item is called

Solar LED driver.

and how to note it down in the accompanying sketch

See the schematic sample above. There is no specific standardized symbol - so use a rectangle as shown with the part-number on it.