Will the iMac support 128gb memory cards

Apple has made 27" iMacs for about 13 years, however I was able to tell you have Nano texture glass which only came out on the 2020 27" iMacs therefore you own a 2020 iMac. If you are going to upgrade the RAM please only use Crucial.com or Macsales.com RAM. Most users DO NOT need anywhere close to 128GB of RAM, however your iMac can accommodate 128GBs of RAM (4 x 32GB DIMMs).

The reason I said to only use Crucial.com or Macsales.com RAM is because iMacs are extremely sensitive to using high quality RAM. Both vendors mentioned offer high quality products, have great prices, offer excellent service and the RAM has a lifetime warranty. In short there is NO reason to not use them. I recommend buying direct from them and not using stores such as Ebay or Amazon.

Good luck.

I have the 2020 10-core i9 iMac. I have 128GB of Micron RAM (via Crucial) installed. 4 @ 32GB ram cards. There were a lot of problems with the 2020 27" iMacs using OWC RAM (I was a victim as well) so make sure you only use RAM made by Micron (an Apple OEM partner) that is sold by Crucial. It will save you a lot of headaches.

OWC is used by MacSales so I would avoid them.

This was a huge support article about how OWC (MacSales) RAM was causing lots of issues.

https://discussions.apple.com/thread/251962728?answerId=254170742022&page=1

While 128GB is quite a lot (and $$), if you have the budget for it then go for it. My workflow (video encoding, professional photography) has me exceeding 64GB RAM so having 128GB helps and is nice to see MacOS never having to resort to a swap file.

No it will not. However you have not told use the model year iMac you own so we cannot tell you anything useful at this point. iMacs have been built for over 20 years now and in hundreds of configurations. Our mind reading skills are awful and everyone here refuses to look over others shoulders so we rely on you to write complete questions. You may benefit by carefully looking over Writing an effective Apple Support Commun… - Apple Community and then re-writing your question.

Just as an aside:

I looked at the thread you linked to - interesting. Over 10 years ago, there was a similar problem: iMacs would be fine with a full max of OEM 16 GB RAM (they came with just 4 GB). They would also be ok with a partial mix of OEM and third party (not just OWC - any third party), but replacing the original 4 GB of OEM with a full 16 GB of third party RAM resulted in major problems. At the time, I and most everyone else fixed it by going to a total of 12 GB mix and that worked well. This was with late 2009/2010/2011 27" iMacs. And, OWC worked diligently with Apple trying to figure out what was causing the problem. Someone did eventually, but I never heard what happened.