Trouble with my iMac playing DVD’s from my external DVD player.

Unfortunately, your Mac is set for region 1. The DVD must be from another region. As mentioned, you only have 5 times to change the region, so you could potentially change it now, but then you need to set it back to region 1 = two out of five "reset"opportunities. And, when you get to # 5, you will not be able to change it at all - meaning that whatever region is active will stay in that region.

#2 - until now all DVDs must have been from Region 1.

#3 - if you live in Region 1 then only purchase DVDs for that region.

#4 - you can't. They are build into the software. But you might be able to use VLC as babowa suggested. It's free so give it a try.

The DVD Player app that came with Catalina, Big Sur and even Monterey works fine with those systems.

Download and run the free GO64 app. After running do search for Preview and see whether it's 64 bit or not.

This is what it shows for the new beta system:

However, I did notice that to get it to play a video DVD one must mount the DVD and then use DVD Player's File ➙ Open DVD Media…" menu.

It should open the Video_TS folder in the next window. Just click Open and it will run. (This is on non-commercial video DVDs that I created). Don't have any commercial ones to test at this time.

The problem is that the computer and/or drive are set for a region and if you can't change the region (as shown in your screen shot), then you are out of luck. The only DVD you can use would be one that matches that region. There are DVD players that will play any DVD from any region, but they are not only hard to find, but also very costly. Unless you need this for a business, it is most likely not worth it.

But, even if you got one, you still have the problem with the embedded restrictions on your Mac......

4 The embedded restrictions regarding the regions cannot be removed - it's the built in software (DVD player app) and OS that is set to regions. You can try to use VLC (download the app) which will play about anything.

You may also run into the same/similar problems with newer commercial DVDs. I borrowed one at the library once and it would play in a stand alone player, but not on my iMac. I can only guess that the problem was: on a computer, you are able to copy a movie with the right software - the companies see that as piracy and do whatever possible to make it impossible for you.

As for 1 - you may have had DVDs that happen to be the same region as the player? Otherwise, I do not have an answer for it.

2 and 3 - I do not have an answer for it; maybe someone else will chime in.

I have a similar problem when moving up to catalina, The DvD player (provided by apple)needs updating, but there is no updated as the dvd player appears to be a32 bit app. So I might as well trash the two mac minis that I use fro my entertainment system as I can no longer watch DVDs thus they force you to buy from apple TV...they did this sort of thing before and lost millions in revenue when customer started sending ne computers back as the were not fit for purpose...