chromium snap cannot open external apps by uri using xdg-open

UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) snap Chromium/78.0.3904.97 Chrome/78.0.3904.97 Safari/537.36

Steps to reproduce the problem:
0.run chromium snap on ubuntu
1.open page with link like tg://resolve?domain=abcd&post=123
2.click the link
3.the dialog opens, click "open xdg-open" button

What is the expected behavior?
the system default app must open the link (telegram app in this case)

What went wrong?
after step 3, nothing happens.

if chromium is run from terminal, one may see in terminal the following text:

user-open error: Supplied URL scheme "tg" is not allowed

Did this work before? Yes ubuntu 19.04, in apt-chromium

Chrome version: 78.0.3904.97 Channel: stable
OS Version: ubuntu 19.10

pls note that the same link opens fine when clicked from "usual" apt chromium package (tested on both apt- and snap-chromium on ubuntu 19.04, and on snap-chromium on 19.10).

correctly working apt-chromium package was available till ubuntu 19.04. now, since ubuntu 19.10, only snap-version of chromium is available which is broken

i've already posted this bug on chromium bug tracker:
https://bugs.chromium.org/p/chromium/issues/detail?id=1023216#c2
chromium's team member replied:
Status: WontFix
We don't maintain or build the snap distribution. You'll have to open an issue on ubuntu's bug reporting tool against this.