So far, I used the most portable format I can think of: the command-line-based format:
importdescriptors "[{\"desc\":\"tr(cMahea7zqjxrtgAbB7LSGbcQUr1uX1ojuat9jZodMN87JcbXMTcA)#tnrke5yz\",\"timestamp\":\"now\",\"label\":\"taproot\"}]"
importdescriptors "[{\"desc\":\"tr(cMahea7zqjxrtgAbB7LSGbcQUr1uX1ojuat9jZodMN87K7XCyj5v)#xpd75frm\",\"timestamp\":\"now\",\"label\":\"taproot2\"}]"
It is standardized across wallets, it is extensible, and it is reasonably-compatible between different versions of Bitcoin Core. Also, in case of incompatibility, it is quite easy to fix it, and convert into another version of Bitcoin Core.