Can a PC player join a PS4/5 player, even if they aren't the host of the world?

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today Selina

Only the person who created the world can give you access to it :c
In this case there's no workaround sorry

If you have further questions feel free to ask, greetings from another Microsoft user

We experience a complete freeze. When the account that freezes is hosting the world in splitscreen, all players and the world freeze.

When the account that freezes is the second player, not hosting the world, no one freezes.

When the account that freezes is hosting a world on xbox, and I join on my PC, only the xbox player freezes. I do not freeze on my PC, and the world does not freeze.

Hope this helps. Please let me know if you need anymore information.

Also, in the host settings you can choose what other players are able to do in your game. You can also grant permissions to each player when they join. While it may get tiring having to give each player that joins the permissions you have decided for them,
when a random player joins they will not be able to make any changes to your world.

In Minecraft, the world is saved to the account that is "Player 1" and starts the game first.

When the second player joins that world, he is saved together with the world in Player 1's save slot.

If the second player starts the game themselves, they start a new game with a new world and empty inventory, as they have no access to Player 1's savegame. To prevent that, make sure that Player 1 starts Minecraft and enters their world, and that Player
2 then joins that session.

If you want the two players to be able to play independently on the same world, you would need to rent (and pay for) a Realm that is hosted on Minecraft's online service.

Players on PlayStation 4 and Xbox One can play with and against each other, but not with players on PC, PlayStation 5 or Xbox Series X|S - even with cross-play turned on.

PC is not crossplay with console (ps4/xbox one) on this or any battlefield game.