Speaking from a production and legal standpoint:
Since Sony can only use characters related to Spider-Man (So never MCU characters, not locations, nor events, etc.), and Spider-Man himself. Their movies will never become part of the MCU proper (Meaning the universe where we see the movies take place) since there is no coordination or worldbuilding.
Conversely Marvel Studios is not able to use live-action characters from Spider-Man (Not even Spider-Man himself) without permission from Sony, so it's highly unlikely they will ever use Venom or Morbius; since they'd need permission from Sony (See the What If... episode with Survivor Spider-Man for an example of the lengths they'd go before that.)
The Sony Universe will try to appear as if it was MCU but will start showing the seams (Timeline -MCU is ahead some years-, no references to big events in the MCU, no organizations of the MCU, concepts of powers are off-limits -mutants, specific magic-, etc.)
Regarding Venom's post credits, I think the most likely scenario is that it won't be referenced not even in Venom 3 (Like the wig in the last one :v ). It was most likely trying to tie-in into No Way Home hype.
Potential spoilers from No Way Home leaks: And so far the indication is that Venom isn't part of the Sinister Six, nor appears in the movie. And even if Venom appears in a post-credits scene, it would never have a follow-up in the MCU proper.
The most likely appearance of Venom and Spider-Man together will be Venom 3, since it's where Sony keeps 100% of the profits.
Think of Spider-Man in the Sony's SUMC as a Variant Spider-Man where events depicted in the Marvel Studios Spider-Man movies happened (Like Peter unmasking, but not anything else, i.e. The Blip)
And IF Venom appears in a post-credits scene, think as a Variant Venom, who will never be seen again in the MCU
The perfect example is Agents of SHIELD where nothing that happened there ever mattered to the worldbuilding / was referenced in the Marvel Studios productions.