Others may already be aware of this, but after a year of playing single player without using the Galaxy client, I learned about one aspect of multiplayer the hard way:

In the multiplayer game, it is possible to have combat with other players, an option currently enabled by default. There is at least one (and probably a lot more) "griefer" playing NMS. The one I encountered fired a lethal weapon and then waited for the dying cutscene to end. Then he or she fired again--and as most know, a second death before the contents of the grave have been recovered means that the exosuit's inventory is gone.

Here's what I discovered about preventing this: when, to get multiplayer mode, you launch NMS from GOG Galaxy, you'll see an options box in the lower left. Those options are NOT the same as the options Hello Games built into the game. To block player vs player combat, wait until the game loads and then go to the in-game options. Under "Network," you'll see a "PVP" option. You can select "Allow with No One" (or "Only with friends," etc.). That may well save your game.

While it is true that there may be griefers in NMS, as in any game, from my experience most such deaths are actually accidental, due to the AoE nature of the Neutron Cannon, which is very popular and arguably the best weapon in the current version. Its blast radius is deceptively high and the damage dealt is usually enough to kill most players in one hit, depending on upgrades ofc.

So it is always good to turn PvP off as soon as a new save is created (normal, expeditions or whatever) in the way described by the OP.

I'd like to think your "most" is true, but those who wait and fire a second time clearly intend to kill someone's game. For what it's worth, I discovered many recent (18 hours before my post here today) posts about this on Reddit, all talking about the "shoot twice" griefers. I filed a suggestion with Hello Games--that "PVP be disabled by default--on Nov.19, and was glad to see the Reddit posters suggesting the same thing. Perhaps at some point, Hello Games will get the message. There always will be vandals (in games and in real life), but in this case, a simple measure would stop them from interfering with others.

I'm not sure links outside GOG are allowed, but here's the Reddit post I ran across: https://www.reddit.com/r/NoMansSkyTheGame/comments/18kwouw/expedition_murder/

I did not mean to sound dismissive of the valid concerns related to griefing, it is sadly natural that such behaviours emerge in videogames of all kinds, mostly due to the anonymity and impunity the internet provides.

I only meant to add my own personal experience that avoiding pking ur own friends is next to impossible given the AoE nature of the neutron cannon, unless ofc pvp damage has been toggled off in advance, which cannot really be expected of all strangers met in the anomaly to have done.

The solution to both issues is ofc the very simple one, suggested by you and countless others over the years: have pvp damage disabled by default.