How can I encrypt USB drive so that it would subsequently be readable/writable on any computer that I plug it in? For instance, it should then be possible to easily plug the encrypted USB drive on a Windows or Mac computer, and be able to access the contents without any fuss.
As for the solution to encrypt a USB drive on a cross-platform, I guess a third-party utility is the optimal option, which supports sorts of operating systems. If you plan to encrypt a USB drive on macOS and Windows, iBoysoft BitLocker for Mac is suggested here, which allows you to encrypt USB drive on a Mac without a hitch as your Windows PC supports BitLocker drive encryption.
Take care~
This is a guide on how to enter Target Disk Mode on Intel Mac & Apple silicon M1/M2/M3 Mac, and how to fix Target Disk Mode not working.
An explanation of the system report on Mac, it also guides on how to check system report/system information in macOS Ventura and how to use the Mac system report.