I'd be looking for some additional consideration to increase a notice period.
At my old place my notice was tied to service. It started at 1 month rising to 6 when I'd been there 10years. It was mutual. It worked, some people did very well out of it with redundancy.
I left last year and shortened my notice period back to 3 months. My new employer wanted an earlier start but we're prepared to wait if needed. After all the negotiation on both sides, covid hit and I went back and un negotiated to 6 months!
I'm now on 1 month again. But this is short for the industry. 3 months is more normal.
It might vary in company size. As a large multinational my last place wasn't going to collapse when I left. The negotiation included what was to be handed over and how.
In a smaller company one significant person leaving has a much larger impact.
