I’ve had trouble doing this for bot accounts hosted on sportsbots.xyz. Not actually sure if it’s possible with them or not as you can’t access their feeds from that site.
For instance, I use mastodon.world and can access Fabrizio Romano’s feed via mastodon.world/@FabrizioRomano - but adding .rss on the end doesn’t seem to work, nor does sportsbots.xyz/@FabrizioRomano.rss