Can I see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50? Is it possible to see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50? And even the moon?
This is the description of the telescope:

User-friendly and easy to install with magnification up to 100x.
A telescope is a learning and discovery tool that is suitable for both old and young. This model is larger and has significantly better optics than the telescope that Galileo Galilei used during his astronomical discoveries hundreds of years ago. Magnifies from 30-100x. The viewfinder binoculars (5x24 mm) make it easy to roughly calibrate the telescope and the stand is easy to mount. Focal length 600 mm. Light opening 50 mm. Weight about 3.1 kg. Live incl. 2 eyepieces.**
Generally speaking, you should never buy any telescope which advertises itself in terms of magnification.
Telescopes at this level are, unfortunately, not much more than toys which will serve more to frustrate than to delight.
These telescopes are made almost exclusively from plastic parts - the optical tube, the focuser, even the eyepieces are a polymer and not a glass. The tripods are flimsy aluminium.

If you only have €50 to spend then you could buy a pair of 8x42 or 10x50 binoculars. At this price they won't be a great pair of binoculars, but they'll show you a lot of objects in the night sky which you can't see with the naked eye alone.
More positive points in favour of binoculars:

you can use them during the day
they're very portable
they'll continue to be useful as you continue in the hobby --- I still use my €40 10x50s to sweep the sky even though I have a reflector and a refractor; each instrument gives a different view


Alternatively, you could put that €50 into a savings account and then try to add to it at every opportunity you get. Your goal would be to save up around €200
A telescope which is generally accepted as being one of the best starter telescopes is a 130mm F5 reflector sold in the USA under the name &quot;Astronomers Without Borders OneSky&quot; and in Europe under Sky Watcher brand with the name &quot;Heritage 130p&quot;.
It's a Newtonian reflector on a Dobsonian mount. It has an aperture which is large enough to show you details on Jupiter, Saturn, and Mars (around opposition, at least).

In between the €50 binoculars and the €200 reflector there are many achromatic refractors, but I hesitate to recommend any of these because you mainly want to observe planets:
When light passes through a refracting telescope's objective lens, different wavelengths are diffracted different amounts, and this results in some colour separation which is most noticeable with bright objects.
Planets are some of the brightest objects we observe.

Also, many of the aforementioned refractors also suffer from less-than-brilliant build quality, which is another reason to go for the the 130mm reflector. Here's how I think about it:
At this price point you want to make sure that as much of your money as possible is going into what's important: the optics.
Anything else: bundled eyepieces, diagonals, tripods, equatorial mounts, ...all of this costs money, and money going into these components is money that isn't going into the optics.
This is why a Newtonian reflector on a Dobsonian makes the most sense: the optics are mirrors and the mount is a couple of bits of wood. Telescopes don't get any more simple than that :-)

You mentioned in a comment that it was hard to find the Heritage 130p in Europe.
Right now it's hard to find any telescopes anywhere - the pandemic has created a lot of new amateur astronomers and has also affected supply from China.
Here's a short list of European shops I can think of which you might want to check out:

Astroshop
Bresser
First Light Optics
Teleskop Service

Of these, if you're looking for good deals then keep and eye on Bresser's and FLO's special offers pages. (If you're in the EU then be careful ordering from FLO because they're based in the UK and you'll have to pay additional taxes on your orders). Bresser is probably the place where I've managed to get the best deals.
Finally, consider buying second-hand. Your money will go a lot further.