5 each CDRs burned 2001 will not open

Apple dropped all support for the HFS (no "+") filesystem in Catalina and later.

Reportedly, Macs running Catalina and later will reject all optical discs that have HFS filesystems on them, including hybrid discs that were explicitly written with two filesystems so that they could be read on a Windows PC. Although the modern Macs might be capable of reading the filesystem meant for Windows PCs, when they see the HFS one, they choke and reject the disc.

Thus if you have an old optical disc written by a Mac that is in perfectly good condition, you might have more luck reading it on a Windows PC than on a modern Mac. A truly sad state of affairs.

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Quite apart from that, CD-Rs don't necessarily last as long as people thought they would. The aluminum layer on a factory-pressed CD or DVD may last a long time – but the dye layer on a recordable disk might deteriorate after 10 years. You say that you burned your discs in 2001 (about 23 years ago), so it is possible that they have gone bad – especially if you have been storing them in any place where they would be exposed to a lot of heat.

You can try using a Linux system to see if it can read the CDs. Linux is able to read the old Apple file systems, although with some distributions the necessary drivers and/or software may need to be installed from the Linux distribution's software repository.

The easiest option may be to create & use a bootable Knoppix USB stick. IIRC, Knoppix has the older Apple file system drivers installed by default, but it has been a while since I tried to access the older Apple file systems. Knoppix should be able to boot any 2007 to 2015/17 Mac (without USB-C ports & do not use a 2006 MacBook with the 32bit Core Duo CPU or it may damage that specific model laptop), or most any PC using a decent CPU. Booting from a Knoppix USB stick should not affect the data on the internal drive because the Knoppix default is not to automatically mount any volumes. If you try to boot a Knoppix USB stick on an Intel Mac, then you must give it time to boot since the Mac may appear frozen on the Apple boot picker menu due to how Knoppix boots & the Mac's very limited firmware. It can sometimes be tricky getting a Linux USB stick to boot to boot on some UEFI booting PCs due to poor UEFI implementations for selecting boot media. It is possible to boot recent versions of Knoppix even if the PC has Secure Boot enabled, but you must select the proper bootloader file (I think it may be the bottom one on the list of boot files).

You can try using data recovery software to attempt to recover the files if the CDs are damaged.

Try using the v9.1 Knoppix .iso file with "EN" in the name for ENglish. Either the CD or DVD version should be Ok although the DVD version will contain more items, but IIRC the CD version used to have the necessary drivers installed by default. Even if they are not installed by default, it is easy enough to install them if using the most recent version of Knoppix.

To create a bootable Knoppix USB stick you can use the downloaded Knoppix .iso file as a source for Etcher (Mac, Windows, Linux). Or you can burn the .iso image to a CD/DVD (you do not burn the .iso file to CD/DVD, but burn the contents of the .iso file to the CD/DVD). It has been over a decade since I burned a CD/DVD, but on macOS I believe you need to use a third party app such as Toast since macOS is usually unable to mount or process Linux .iso files.

The other Knoppix files listed are used to confirm the integrity of the .iso file to make sure the download process did not corrupt the file & the file has not been tampered with after creation. You need to use a utility to create a hash of the downloaded .iso file & compare it to the respective file.....macOS & Windows both have built-in command line utilities to do this. The files with "DE" in the name are for German (DEutche).

That's an ancient Disk/Disc format, I doubt you'll be able to read them, but see this for clues..

Mac CD reading as a ProDos disk - Apple Community

Possibly an old pre OS9 mac, or maybe an Emulator...

converting ProDOS files - Apple Community

CDs or DVDs?

Regardless of formatting, burnable optical disks are not permanent. They are not like "pressed" app, music and movie disks. Burnable disks have photo-sensitive dyes that will degrade with time. This article has a very good illustrated explanation of the difference between pressed CDs and writeable ones. Very different technologies:

http://techref.massmind.org/techref/cdrs.htm

This one:

https://www.howtogeek.com/682807/the-cds-you-burned-are-going-bad-heres-what-you-need-to-do/

has some info and storage recommendations which says UV light can degrade the writeable layer and cause loss of data. Other source find that, with proper storage, burnable CDs can last up to 100 years; with improper storage they can be useless in as short as fve years. Yours are 23 years old.

Where were they stored? I hope you don't say "the attic." 😱

sgcnostromo wrote:

Today I did locate a 2006 Gateway laptop running Windows XP

That machine may even allow (a CD in) an HFS format to be read, provided that an appropriate version of a Windows utility for Mac disks (such as TransMac or MacDisk) is used.

Regarding picture #4: This does not have to mean that the discs actually were made in a ProDOS format. I have earlier noticed the same message with an old CD-R that refused to be recognised. After many more attempts, it finally appeared as a readable Mac OS Standard disc on the Desktop of a Mac OS 8.6 iMac G3. So, you could perhaps check whether inserting a CD ten, twenty, or even thirty times would change anything.