Germany: Is it legal to connect a gas oven to a gas tank manually?
Update: the stove you refer to is an outdoor gas stove. You don't even need to talk to anyone, using thas stove indoors will violate all kinds of regulations and will pose a huge safety hazard to you.  There are also better ways of killing yourself than running an outdoor gas stove indoors.
Unfortunately Ooni doesn't give the power of the stove on their web site, but they say that 440 g of propane (1 lb) will last &quot;up to an hour&quot;. Propane has a lower heating value of 46 MJ/kg. At 440 g/h that is 20 kW. I.e. you are far above the 11 kW limit for normal private use of gas burners in a flat.
BTW: you don't need high power to reach high temperature in the stove if the stove has decent insulation and/or a volume that is not much larger than the pizza. For indoor settings such insulation is not only required for gas safety reasons but also for fire and burn safety.
To give you an idea, a quick glance found me that a 20 kW gas indoor pizza stove is the size for making 9 30 cm pizzas simultaneously.  Or, thinking from the other side, you get electric indoor pizza stoves with   2.5 - 3.5 kW (suitable for 230 V 16 A i.e. standard electric installation) for a single pizza at a time.


If the kitchen is equipped with a plug-in gas outlet, you plug in your new stove and proceed as the manual says.

If there is no fixed gas installation available, the bottom line is that hardly anyone cares about the hassle (safety plus safety burocracy plus carrying gas bottles into your flat) and people go for electric (e.g. induction) cooking instead: the electric installatin typically has 3 phases with 16 A for the electric stove, so you can get 11 kW electric stove as easily as an 11 kW gas stove (gas installation above 11 kW has additional regulation).



Otherwise:

If you are not owning the house, you'll have to talk to your landlord. It is quite possible for the renting contract (or the landlord) to forbid gas cooking for general safety reasons. (If you own a flat in a house, you may have to talk to the other owners, but there I'm not sure)

Where the building has a fixed gas installation, a rental flat typically comes with a fixed gas stove already installed.


Building and fire safety regulations vary by Land (state, province).

You may need to obtain the permission by the chimney sweeper, and have them regularly measure emissions.
Make sure you talk to them beforehand since they may tell you that you need to put ventilation holes into all doors etc.
One important limit is 11 kW - below that things are somewhat easier, but you still need to take care of regulations like minimum distances and required room volume.
You can also ask the customer service of the local gas provider (Stadtwerke) about regulations. They'll know even if your house is not connected with gas.


For fixed gas installation (gas tank, fixed pipes, fixed connection to stove) call a gas fitter/plumber (in Germany, Gas- und Wasserinstallateur or old name
Klempner = plumber is one profession).

In general, there is also the possibility that you do the installation yourself and then have a plumber do the safety check only. (Similar for electric installation.)
Of course, it is quite possible that no local plumber will sign the safety certificate if they cannot sufficiently inspect the installation. So make sure you talk to them beforehand.

If we're speaking gas bottle and stove, you can connect bottle, reducing valve and stove yourself. Make sure you have the propane nozzle in.  (And if you don't know what I'm talking about, have a plumber show you)
You still need approval by landlord and also the regulations like approval by chimney sweeper, ventilation etc. still apply.
For the technical part of the rules, the Technische Regeln Flüssiggas are relevant.
Keep in mind:

no underground storage of gas bottles, no storage in sleeping rooms etc.*
at most 16 kg of propane or butane in the house (so one 5 kg reserve bottle plus the normal 11 kg bottle)*
you can not fill your gas bottle yourself at the gas station, instead you exchange it for a full one.




* without special installation (e.g. force ventilated gas cabinets)