can i use one external drive for both Catalina and High Sierra bootable drives

Thank you so much. I have never partitioned a disk before, so I am not sure on how to proceed using Disk Utilities. I would really appreciate your listing the steps required to partition an external disk in 2 partitions of the correct Format and Scheme compatible with a 2011 Mac running High Sierra and a 2019 Mac running Catalina? Also, what is the minimum partition size necessary to contain the above bootable drives?

Thank you.

Yes and on the same wifi. But I don't think that should be an issue. I know that the 2011 Max cannot run Catalina and the 2020 Mac cannot run High Sierra. I need bootable drives for each OS in case I need in the future to use them if I have difficulty starting either machine, which I plan to keep both because some of my 32 bit applications will not run on Catalina. This has already happened to my portable 2011 MacPro laptop with High Sierra, which failed to start in any mode, even from the internet, until I borrowed a bootable High Sierra external drive and was able to start it in Target mode.

The cost of an additional drive is not the issue. I would appreciate getting detailed instructions on just how to partition an external drive as I described earlier, which will work with both High Sierra and Catalina. Thank you for your help.

I'try that. Thank you for your help.