It is better to switch to Firefox. But chromium forks can generally do whatever they want, it’s just a matter of maintenance burden. e.g. nothing is stopping a Chromium fork like Brave from running a manifest v2 compatible appstore, but it’ll cost money to make, maintain, and operate, plus you have less discoverability as an app developer when using a smaller app store.
It is better to switch to Firefox. But chromium forks can generally do whatever they want, it’s just a matter of maintenance burden. e.g. nothing is stopping a Chromium fork like Brave from running a manifest v2 compatible appstore, but it’ll cost money to make, maintain, and operate, plus you have less discoverability as an app developer when using a smaller app store.