One of my domains uses the .ch TLD, from Switzerland, I use it for many account registrations via email. Should I be worried that I will lose access and proactively migrate away from this domain?
Realistically I think you're fine sticking with .ch, but consider one of the original gTLDs for future use (com, net, info, org)
If you trust them, it’s fine. I would guess they’ll be around for a while.
That's not entirely true. What happens for ccTLDs is that they're owned by the government, and administrative and technical management of the extension is delegated to a foundation/association. In the example of France (I'm French so I know it best), the .fr has been managed by the Afnic historically, but it's renewed every few years (5 I think?) by the government. Last time was 2021.
In the case of ccTLDs you need to trust the associated government no matter what, more than the delegated registry.