Gdtyjr

Here I found lecture notes in which the author uses the following symbol when a certain thought is finished but no new chapter or similar follows.

Since the user doesn't share his source I code I wondered if

there is a package or good way to produce this symbol or if the standard method is just to insert this symbol as a picture when necessary.

The requested symbol and several other similar ones are part of the package https://ctan.org/pkg/pgfornament. Below is a screenshot from the pages 20 and 21 of the manual. You see that your ornament is symbol number 88. The manual also gives some information on the origin on those drawings.

Here is an actual example to achieve something similar to your example. My understanding is that the symbol is used on points specified by the typesetter and not after every paragraph. The command ornamentSep allows just this.

documentclassarticle
usepackagepgfornament,multicol

%The command itself does not require the package multicol, but the example below does. The command also respects the twocolumn option
newcommandornamentSepnoindenthfilpgfornament[width=0.618033988749895columnwidth,color=red]88

begindocument

titleTitle

authorViktor Glombik\ornamentSep

maketitle

Greetings to Berlin, Viktor. 

ornamentSep

Aut necessitatibus rerum et ea. Aperiam nulla quibusdam neque non voluptatem. Molestiae consequuntur asperiores beatae reprehenderit. Quia ipsum aut veniam quis rerum quos aliquam modi.

ornamentSep

Aut necessitatibus rerum et ea. Aperiam nulla quibusdam neque non voluptatem. Molestiae consequuntur asperiores beatae reprehenderit. Quia ipsum aut veniam quis rerum quos aliquam modi.

ornamentSep

beginmulticols2
Aut necessitatibus rerum et ea. Aperiam nulla quibusdam neque non voluptatem. 

ornamentSep

Aut necessitatibus rerum et ea. Aperiam nulla quibusdam neque non veniam voluptatem. Aperiam nulla quibusdam neque non voluptatem veniam. Molestiae consequuntur asperiores beatae veniam reprehenderit. Quia ipsum aut veniam quis rerum quos aliquam modi. 
endmulticols

enddocument

A quick remark on the OP's comment of March 2019.
The command was designed for central alignment to the text which seems like a natural decision to me. Many canons of page construction for the twoside option set different widths of inner and outer margins. It should be possible to modify my command to adjust the ornament central to the page (if that is what the OP wants). I currently have no idea to do it elegantly and class independent. A dirty solution would be a manual shift like the following modification where you need to adapt the space by yourself

%uses the package changepage
newcommandornamentSep%
ifoddpage%
noindenthspace-4.10cmpgfornament[width=0.5pagewidth,color=red]88%
else%
noindenthspace-5.65cmpgfornament[width=0.5pagewidth,color=blue]88%
fi%

I still believe that this is awkward.