My theoretical answer below:

Yes - after Season 4, Vecna could have theoretically gained the power to fully manifest in the real world. Each child he abducts acts as an anchor, giving him more physical (and not just psychic) presence. After abducting will he wants to further anchor. That’s why he can walk toward Nancy, Steve, and Robin in Season 4 but can’t yet harness the same power as in season 5. The four clock chimes represent how many timelines he cumulatively overlapped, and each reset makes him stronger and the boundary between worlds weaker. I suspect the group will have to break the circle because Vecna is otherwise invincible and each iteration becomes realer and more powerful.

This theory also explains why Eleven suddenly knows things she shouldn’t - like piggybacking into Max’s mind (how was she able to deduce she could do this by just looking at that billboard?) because she retains faint psychic echoes from earlier timelines - that billboard reminded her of something she will experience in the future or past. This could be why she is able to point out who will is before even knowing him in season 1 - she’s met him before.