Is it related to Inception | Loose sequel?

conceptionally, both movies are espionage movies with a scifi element. but that's about it.

I don't think so. Why do people want this? The less connected movie are, the more interesting they have potential to be.

Definitely not related.

Although, Nolan seems to be doing heist movies only, anyway.

Batman, heist movie of criminal doing crazy stuff.
Inception, heist movie in the sub-conscious.
Interstellar, heist movie in space.
Tenet, heist movie in space.

Even Dunkirk could be argued it's a heist movie of saving some soldiers, but it had more things there, so I won't.

It could be argued all of Nolan movies (even TDK trilogy) take place in the same 'universe' similar to Tarantino (or any 'auteur' film director with that style unique of their own)