That's what I did. Just make sure that other node is placed well so it can reach another node.
With the second device I was able to send messages to my city network more reliably, but I still have iaaues when communicating on a private channel with a friend on the other side of the city, even when that friend is theoretically in reach of me in regards to hops.
The antenna in that device isn't that strong. I get the same issue with it sometimes. Either the messages aren't reaching another node, or you are not receiving the acknowledgement response that you message was passed on to another node.
Editing comments after posting doesn't seem to work. Comment box flashes but still shows the original comment.
Yep, that sounds exactly like what I'm seeing.
On another note, reading your reply in the Summit inbox and tapping on "go to post" in the context section results in the following error:
Client error. Code: 400. Message: missing parameters for post.
My "All subscribed" feed contain posts from several non-subscribed communities when logged into piefed.zip.
I'm also not that experienced with Meshtastic, or radio communication in general, but I think you should consider another antenna for a few reasons.
The size is a bit small. At least it looks like it from the pictures. The description says 36 cm, but that's including the connection cable which you won't use on your T-Deck, right? It's probably incorrect to say that a longer antenna is always better, but I've solved issues with one of my Meshtastic devices by increasing the size of the antenna a few times.
It's made of fiberglass. There are flexible antennas which I think would fit better with the portable nature of your T-Deck. I couldn't find one on the website you linked, unfortunately, but just searching for "868MHz Antenna" on Amazon/Aliexpress should give you some results like this:
The price is quite steep. 45€ vs ~10€ for other options.
And least important point, it's white, but your T-Deck is dark gray I assume?