Google Domains, which I use as my domain registrar, apparently limits you to one TXT record per subdomain. Most service providers (including Google) require you to put a TXT record in your top level domain with a code they give you to prove you own the network. If I also want to implement DKIM or SPF, I can't do so without removing the code.

Google's support has been very unhelpful (I think it's some guy in India reading off a script), just telling me that they do not allow multiple TXT records per name. Name is what they call the subdomain, apparently. Why on earth not? Surely I can't be the first person to run into this limitation? How do others deal with it?