install previous MacOS (external drive) to use 32bit apps

[foxymac]

I have a 2018 MacBook Air with latest Catalina on the internal SSD, crypted by the T2 chip.
I have noticed that some games that in the last years I loved to play, have stopped to run under a full 64bit OS (for example, doom3 and quake4 from the AppStore, and in the Steam Library, games like HL and HL2 saga, my favorites).

I found on the net people that say if I install High Sierra on an external drive (my Mac has USB-C ports) I can then put there the software I want to use.

I have questions.

If I have a thumb drive I've made to install HS, may I install on external drive, even if I have a T2 Chip? and maybe crypt also the external drive (or not?) ?

And may I choose where to boot (with Option key) as I used to do on various friends' Macs?

I hope that someone could give me precious hints.

 

[Ritsuka]

Yes, you can install 10.14 on an external disk. You need to enable booting from external disk and maybe set security to medium: https://support.apple.com/en-us/HT208198

 

[foxymac]

Thanks! it was kind of a mess, because it implies to disable the T2 security... but in a hard way, it worked.

 

[The Man]

Here is a direct link to Mojave if you need it.

https://itunes.apple.com/us/app/macos-mojave/id1398502828?ls=1&mt=12