How do make Twitter display bigger image when sharing blog post?

Site URL: https://computerclub.online/afleveringen/107-applegaming-flash

When I share a blogpost URL to Twitter, it shows a small image in the Twitter card, rather than a big visual.
Please see the attached files for the current vs. desired look.

I have a thumbnail image set (900 x 600, width x height), and an alternate social image (1200 x 628).
I also have an Excerpt text set, and a SEO Description.

When I share to LinkedIn or Facebook, it does work (i.e. it shows the bigger preview).

Already tried the Twitter Card Validator, see attach.

Thanks in advance,

Freddy

I have the same problem. Did you get any help?

I also have the same problem. Does anyone know how to fix this?

Are there any updates on this? I have the same problem as well. 

I have the same problem, and squarespace does not seem to care. It's a ridiculous thing that has a huge impact on website visits.  

I have the same problem. How do I fix this?

Same problem and doesn’t look like Squarespace cares all that much - Opengraph is the solution with those with coding experience https://kaydee.net/blog/open-graph-image/ but unless you have upgraded there isn’t a way to insert code.