Quite unexpected I have encoutered the following issues: starting yesterday from scratch with a new map my player had not portal gun (which is exactly what I want because the player should pick up the gun in a later level) but after renaming the map the gun spawns automatically in my hand

I have already tried to place a trigger_weapon_strip at the spawn location but it is only activated after going in and not at MapSpawn. Is there any way to combine this with a logic_auto so that the player does NOT see that he had a gun in his hand?

Did you rename the map so it started with "sp_"? If you do that the player will spawn with a portal gun no matter what. The best way to make the player spawn without a portal gun is to have a map name without "sp_". If you really want to have "sp_" in your map name, I recommend you to use an env_fade to fade in the map while the portal gun gets removed (you can still hear the sound though).

This was indeed the issue - I removed the "sp_" at thebeginning to have "p2m_chamber00" left and it works like expected

my map doesnt have sp_ at the front and I end up getting the damn gun. I wanted the player to collect it later on.