how can I play both region 1 and region 2 DVD

The Region setting is stored in the drive's firmware. When you change the region, the firmware is updated. With a DVD drive on a computer you can change the region up to 5 times, and the 5th change becomes permanent. It's a copyright/licensing issue that all the vendors agreed on long ago.

Here is some more info -

What are DVD region codes?

Change your DVD drive region in DVD Player on Mac - Apple Support

stumpy1946 wrote:

You drive is not going to be able to sense what country you live in.

That's correct, but irrelevant. DVDs are coded with a region code. The drive will be locked to one and only one region code. Once locked, DVDs from other regions will not play in it.

If you have a collection of disks from region 1 and region 2, you will need 2 drives to play them all, one for the region 1 disks and one for the region 2 disk.

You should be able to. I believe the region setting is locked to the drive itself.

Yes, you can have one optical drive for Region 1 and one for Region 2. However, I would recommend getting a drawer loading optical drive from OWC that's self powered. The will have a faster interface than the old Super Drive and reduce the load on the Mac's bus.

Just some food for thought.

You drive is not going to be able to sense what country you live in.

The solution is use VLC (Video LAN Client) instead of Apple’s DVD Player.

To make this work you must go into System Preferences for DVD Movie and either set VLC as the default application or set it to ignore. This will cause OS X to think of the non-Region 1 DVD as a data disk and mount it in the Finder. VLC doesn’t query region code and will just play the movie, though the interface is nowhere near as nice as Apple’s, and there are some stability issues.

Also how to set a DVD drive for Region 0...

https://lowendmac.com/2006/how-to-make-your-mac-region-free-for-dvd-viewing/#:~:text=The%20solution%20is%20use%20VLC,mount%20it%20in%20the%20Finder.