If you have an EKZ electricity provider, you could also obtain a balcony solar power plant with subsidies (valid from June 2022 to December 2022). Without a permit, up to 600 watts could then be connected directly, and the system could also be used to supply other consumers in a flat with electricity, for example. If a solution for stationary operation were to come into question, this would certainly be an interesting alternative to only 50 watts.

Enter the keywords 'solar panel 5v usb output' into Google and you will find what you are looking for :-)
Apart from that, I can only agree with the two previous answers: instead of an adapter, it makes more sense to buy a power station with an 8mm input.
Reason: solar panels emit between 18 -24 volts (at maximum solar radiation), which requires a voltage adjustment for USB.
At the last minute I only found an adapter with 'MC4' plugs --> https://solarpowersupply.de/zubehor...
You would have to buy another adapter '8mm to MC4', e.g. this --> Wattstunde AK-MC-7909 adapter cable (solar cable)

Hello.
The 50w boulder solar panel can only be plugged into Goal Zero power stations with an 8mm plug. The 50w Sherpa folding panel from Goal Zero has an extra usb A output. This can be used to charge all powerbanks.