"This is my door."
Translation:Das ist meine Tür.
I remember that it is 'die' because going through a door is a change of location and 'die Tür' sounds like 'detour.' lol
In German, both 'das' and 'diese' can be translated as 'this'. I believe that in speech, 'diese' is rarely used since it's easy to show 'this' vs 'that'. It's more common in writing, since it's harder to explain 'this' vs 'that'.
From what I've picked up in other threads, as long as the noun doesn't immediately follow, das can be used no matter the gender or how many
Dieses is used in front of a neuter noun: Dieses Haus ist schön = "This house is nice"
Diese is used in front of a feminine or plural noun: Diese Tür ist geschlossen = "This door is locked"
If you don't have a noun directly after it, then you use dies: Dies sind meine Kinder = "These are my children"
Tür is feminine, but dieses is for neuter nouns. It doesn't fit together.
Better is Dies ist meine Tür. That's like saying "This is my door", where "this" doesn't have any 'gender information' on it at all. If you say Diese ist meine Tür you're more strongly giving information to "this", making it more like "This door is my door" or at least "This one is my door".