Is it possible to use ttrss with several domains?

If I understand correctly, this line from config.php
define('SELF_URL_PATH', 'https://mydomain.com');
allows ttrss to be more secure by rejecting all access attempts through other domains.

However, I’d like to be able to access ttrss from more than one domain (e.g. https://mydomain.com and https://myotherdomain.com). I’ve found that I can allow access through any domain by adding this line to config.php:
define('_SKIP_SELF_URL_PATH_CHECKS', true);
but that skips the url check altogether.

Is there any way (through another hidden parameter or something) to give ttrss a list of allowed domains instead of just one?

No.

you can use conditionals in config.php based on whatever you want (i.e. server-provided hostname) to set SELF_URL_PATH or anything else which might differ for your “vhosts”.

note that config.php can also be sourced outside of http server context (i.e. update daemon, etc), so you’ll need to provide fallback versions of the variables.