No

No, Beyonder is a Secret Wars type of character.

I pretty much do not care when any character is introduced.

2 movies left in Phase 5; though not sure if the Beyonder would fit with the cast of either movie.

4 shows in Phase 5 after the current show. might fit with the Spider-Man show since a character in the 1990s cartoon was called the Beyonder.

kind of curious; antagonist or ally?

seemingly an antagonist in Avengers Assemble cartoon.

kind of an ally in 1990s Spider-Man.

While it may seem weird, they could do Secret Wars without Beyonder. No, he doesn’t need to be introduce earlier.

No, while he was a major character for the OG Comics Secret Wars and it's horrible sequel, for the others it was barely apart of the story as for 2015 Secret Wars, it was pretty much the Doom Show for that entire arc.

Plus they don't need him at all. RDJ Doom is probably going to be Emperor Doom at the end of this story arc. He can easy use either He Who Remains or God of Stories Loki power to become Emperor Doom. He doesn't needed Beyonder for his plans.

He Who Remains would probably be dead at the time setting of 5th & 6th Avengers.

and currently not sure if there would be any more scenes (on-screen or off-screen) for the Loki of Loki show.

not entirely sure, but all versions of any character might have same capabilities as any of the other versions. this is pretty much just speculation.

He is most likely to appear in Secret Wars

Maybe