simply being a proportional representation parliament didn’t stop far right parties from gaining power

No. Because the power that the far right party accrued came - first and foremost - from the German military officers' corpse and their allies in private industry. The original Beer Hall Putsch wasn't the result of an election, it was a straight coup. And the leader of that insurrection got turned into a national martyr by propagandists and right-wing agitators thanks to good old fashioned jackboots-on-the-ground rabble rousing.

The German populace was ripe for this kind of agitprop because so many of them - not unfairly - considered their dire economic condition the consequence of foreign government officials who were siphoning off national wealth to profit private industry abroad. This, combined with the White Terror of the 30s to suppress union organizing and the enormous outside investment by American and British Fascists, gave the German movement the legs it needed to compete politically on a national stage.

in first past they may have had far less seats

Largely dependent on the distribution of voters across districts. Historically, FPTP combined with an aggressive gerrymandering of districts, creates seats that are safer for incumbents. But, as we saw in the States, these "safe" seats are still vulnerable to intra-party insurrection.

But all this is secondary to the rapid incorporation of the German Friekorps into the Nazi movement. This gave the party the kind of military muscle that made the election a secondary concern. Even if the Nazis hadn't won a plurality of seats, they could have just as easily used the organized violence of the state militia to extract concessions through another coup (or at least the threat of one).