Can I apply for a DTV visa while in Thailand on a guardian visa?

You can prepare all documents in the eVisa application when you not out of Thailand yet. and submit your documents when you arrive in the other country. Going through the immigration and obtaining an exit stamp as previously said in the comments is *wrong*. If you need help, let me know, We can help you get DTV visa with full refund if your visa get rejected.👍

𝗰𝗮𝗻 𝗜 𝗮𝗹𝗿𝗲𝗮𝗱𝘆 𝘀𝘁𝗮𝗿𝘁 𝘁𝗵𝗲 𝗮𝗽𝗽𝗹𝗶𝗰𝗮𝘁𝗶𝗼𝗻 𝗻𝗼𝘄 𝘄𝗵𝗶𝗹𝗲 𝗽𝗵𝘆𝘀𝗶𝗰𝗮𝗹𝗹𝘆 𝗯𝗲𝗶𝗻𝗴 𝗶𝗻 𝗧𝗵𝗮𝗶𝗹𝗮𝗻𝗱?

You can START the application, make a profile, log in to the eVisa online system, upload all the documentation required and then SAVE that application without applying until you exit thailand

𝗜 𝗰𝗮𝗻 𝗽𝗿𝗼𝘃𝗶𝗱𝗲 𝗮𝗹𝗹 𝘁𝗵𝗲 𝗻𝗲𝗰𝗲𝘀𝘀𝗮𝗿𝘆 𝗽𝗮𝗽𝗲𝗿𝘄𝗼𝗿𝗸 𝘀𝗵𝗼𝘄𝗶𝗻𝗴 𝗽𝗿𝗼𝗼𝗳 𝗼𝗳 𝗿𝗲𝘀𝗶𝗱𝗲𝗻𝗰𝘆 𝗮𝗯𝗿𝗼𝗮𝗱( (𝗶𝗻 𝗺𝘆 𝗵𝗼𝗺𝗲 𝗰𝗼𝘂𝗻𝘁𝗿𝘆).

Are you physically going back TO your home country to apply for the DTV <- because you have to be IN the country of the thai consulate you're using for the application.

Unless you're going back to your country, just go to a nearby country and apply thru a thai consulate once you're there and can upload the visa/entry stamp showing you're legally allowed to be IN that country (that's all they require as far as "residence"

Yes you can start the process, and when you are in the country you plan to apply through add your entry stamps and passport pages etc and submit.