Addition: Sorry, @Sauli_Vilen, for the long, rambling response. These are complex matters that would be so much easier to explain face-to-face or with a PowerPoint. At least for me 
Raising podcasts on the Inderes website’s feed is one good way. It doesn’t require much effort and doesn’t burden the reader with “unnecessary noise.” On the other hand, it’s also very inefficient, as the mention easily gets lost in the stream and doesn’t provide any incentive: why would I listen to this particular podcast today? The highlight happens in the style of: Valio Milk 1 liter. Still, this is a good idea.
Another good way, which you are already doing, is to bring up old podcasts with videos. For example, Verneri has repeatedly promoted the gaming company podcast when a video’s topic has touched upon it. Even in those promotions, you need to be careful: what more do I get compared to this video by listening to that podcast? I think Verneri has succeeded quite well in this.
A mere mention “we also have a podcast on the topic” and a link in the video description is, again, very inefficient. An investor has opened this video, meaning they have perhaps 10-20 minutes to watch the video. Is it a stroke of luck that they now have an hour to listen to a podcast at the same time? Unlikely. Will they remember the advertised podcast during their evening run or find it conveniently? What was the number and what was the name?
Instead of podcast mentions being slapped next to other content, there should be some media specifically designed for them. Here, I think there would be an excellent opportunity to utilize Twitter and Instagram, where your strategy desperately needs a change. In short, it would always be good to operate on the terms and strengths of each social media platform, rather than making the platform serve the needs of your own content. (When there is slightly different content everywhere, you also reach many different kinds of people.)
In practice, this new kind of podcast media should be highlighted when, for example, something significant happens that people are talking about, and you have a podcast ready for it. For example, interest rate worries, inflation, or a market crash. This new communication model would include a short summary of what is happening now and a tip to the podcast.
This way, the content consumer is already fertile ground for a podcast tip and additional information on the topic, as they wouldn’t otherwise be consuming this content. If the podcast isn’t interesting, they received pleasant content from the brief situational description, and it wasn’t just an annoying advertisement. You, in turn, get more value out of already produced material. Everyone wins here.
I could talk about this topic and the utilization of Instagram until I pass out, but this message is already too long. However, I absolutely agree that the podcast archive is a treasure trove that you are not yet exploiting to its full potential. The monetary potential is difficult to estimate, but it certainly adds a lot of impact.
At least it doesn’t hurt that as many answers as possible are behind the Inderes name and that Inderes is even more present in people’s daily lives.