Doesn't start anymore with nftables firewall rules (with Quasar Framework)

[mYnDstrEAm]

It used to work before I upgraded both Quasar Framework (see quasarframework/quasar#10303) from v1 to v2 and Android Studio.
When I run quasar dev -m capacitor -T android and start the app it just displays white space and after a while the net::ERR_CONNECTION_TIMED_OUT error page.

In Android Studio it shows: E/Capacitor: Unable to load app. Ensure the server is running at http://mylocalip:8080, or modify the appUrl setting in capacitor.config.json (make sure to npx cap copy after to commit changes).. sudo lsof -i | grep -v "ESTABLISHED\|LISTEN shows that mylocalip:347xx->mylocalip:http-alt (SYN_SENT) and some similar connections seem to have a problem and that it also does deviceip:4xxxx->someip:5228 (SYN_SENT) for some reason.

I'm using Debian10/KDE with the nftables firewall and have allowed all localhost traffic with

chain OUTPUT {
		ip saddr 127.0.0.1 ip daddr 127.0.0.1 accept

(same for chain INPUT) and now I even set iif lo accept but it still doesn't work.

Why is that? Is it a Quasar Framework-related problem (which) or do I have to allow some more ports in the firewall (which)?

I tried it with:

ip saddr mylocalip tcp dport http-alt counter packets 0 bytes 0 accept
ip saddr mylocalip tcp sport http-alt counter packets 0 bytes 0 accept

in chain INPUT and

ip daddr mylocalip tcp dport http-alt counter packets 0 bytes 0 accept
ip daddr mylocalip tcp sport http-alt counter packets 0 bytes 0 accept

in chain OUTPUT. But that doesn't make it work.
The lsof command shows me a few entries for qemu-syst TCP mylocalip:3xxxx->mylocalip:http-alt (CLOSE_WAIT) which should be allowed with those rules, shouldn't they?

[mYnDstrEAm]

It was due to the upgrade, so something else than the firewall rules caused it.