While there’s obviously a whole heap of made up fan theories flying around, the time travel angle has just slightly more weight to it for me.
If you dig back through old news reports online, there are a few things that sway me;
Way, way back, George Lucas described knowing what he wanted the film to be about, but how he struggled to find the ancient artefact to base it around. This, to me, suggests his original concept was based around a non historic subject - something more thematic.
Later, there was an article online which claimed the film would be based around the fountain of youth, and that in the later part of it, Indiana Jones would be de-aged digitally.
Then Spielberg dropped out the picture, and there was a quote from the writer saying they couldn’t get the key players to all commit. Spielberg said long ago that he didn’t want to digitally de-age the character.
On top of this, there are several other people online, claiming to have ‘leaked’ information - all of which should obviously be taken with a huge grain of salt - but which all contain some form of time travel related angle to the story. While they could all be trapped in the same echo chamber, there is also the chance that it’s a case of ‘no smoke without fire’.
Then finally, we have the shoot itself. Clear evidence of de-aging technology being used, historical footage being shot, and yet more ‘leaks’ siting time travel.
The thing that’s really pushing it over the edge for me though is the Archimedes angle. His work in astronomy, and how it ties in with the moon landing backdrop. The fact that he studied and lived in Egypt, and the shoot is reported off to Morocco in a few weeks (a place often used as a double for Egypt). And most of all, the suggestion that they are filming the Seige of Syracuse, after which the Romans are recorded as stealing two devices that have resemblance to the Antikythera device - which I see as having a high chance of being that ancient artefact which George Lucas was struggling so hard to find, right back when they were developing the idea originally.
Phew! What a novel