I assume that your source for this image is https://www.quora.com/What-are-the-thre ... -of-Sweden, the reply by Marcus Gustafsson. He says that this image is "From Gozzoburg, showing Sweden." He gives no date. There are actually four crowns in the image, the fourth above the other three, as though suggesting that the fourth crown rules over the other three. That would suggest three former kingdoms supplanted by a fourth.A frieze in Avignon, which is dated to 1336, shall show Swedish heraldry with 3 crowns. Possibly it was arranged for a council in 1337.
About the frieze in Avignon, he says, "I have not got a picture, but the three crowns are also shown for Sweden on a frieze in the Papal palace in Avignon." In other words, the picture you posted is not of anything in Avignon, but rather of something in Gozzoburg. It would be nice to find a picture of the frieze in Avignon, to see how many crowns it has.
Gustafsson argues that the three crowns in Sweden of 1275 would not have represented Sweden, Norway, and Scania (part of Denmark) then:
If so, it remains possible that they represented the three Holy Kings, whose alleged bodies arrived in Koln in 1164. But why would the symbol have traveled north, sometime between 1164 and 1275, to be part of a royal seal? Perhaps at some point before 1164 there were three kingdoms that merged. Or they represented something else, and when Sweden was Christianized they decided to reinterpret them as the Three Holy Kings and removed the fourth crown? That was a usual strategy of the Church: not to destroy places and things of pagan significance, but give them new meaning. I notice that the first archbishopric in Sweden was in precisely 1164 (https://en.wikipedia.org/wiki/Christian ... candinavia). The same reasoning holds for Arthur's 3 crowns, where the three kingdoms of England, Wales, and Scotland seem to me probable for the initial meaning, but that wouldn't have prevented other people from giving the crowns a different interpretation.The seal of Magnus Ladulås appears in an age where it is difficult to see what the three kingdoms should otherwise be. In traditional Swedish history, there was only a rex Gothorum, and a rex Sueonum, so we would have to guess about what an eventual third kingdom would be, (if they are kingdoms.)
For further pictures and discussion, the most intelligent website I find (using Gozzoburg as a search term) is at http://www.hubert-herald.nl/Sverige3.htm. It says:
The arms with the three crowns may be of the Swedish Riksrådet, in the time between the ousting of King Waldemar in 1275 and the election of Magnus Ladulås in 1276.
There were three main officials of that body, apparently. This web-page also gives various predecessor symbols, including pagan ones, and does fit Arthur and the Three Holy Kings into the mix. It also says that Magnus Ladulås only had 2 crowns in his seal, in its second telling of the tale (perhaps by a second author?).