Frankly 90% of my frustrations with Signal come from this client, the experience on mobile is better, although still far from perfect. I'm not a fan of pure web clients but web.whatsapp.com is lightyears ahead of Signal's electron bloated and under-featured mess.
The Android client crops the image when I take a picture through the app. No other application does that so I don't really know why it does it. I suspect it's a bug or maybe a bad setting I flipped by mistake but I can't figure out what's going on.
As far as I can tell when you get a new phone the only way to synchronize message history is to create a local backup on one phone, write down the ~24 digit passphrase, transfer the backup by yourself on the new phone then load it from there. If there's a simpler way I haven't found it.
Also I don't think you can move your "secret key" to the new phone, so you have to re-validate your safety number with them. Maybe there's a way to do all that but if I as a technical user wasn't able to figure it out while actively looking for it I have little hope for the average Facebooker.
There's also no support for WhatsApp-style stickers, URL preview, Youtube embedding and all these bells and whistles that I personally don't care for but I'm sure would be missed by many WhatsApp/messenger users.
You're lucky in this case to be on Android. On iOS, Signal blocks any kind of data backups (both on iTunes or on iCloud). [1] So a new iPhone means starting with no chat histories at all. This was requested a long, long time ago (late 2015) and denied stating security as the reason. [2]
But they've been steadily adding features to both. URL previews were recently added, for instance.
Also, I never take pictures in-app, but I just tried it and I can't reproduce your problem with the Android client: there is no cropping on my phone. Maybe an issue with your phone?
It's possible of course but this is a fully updated Nokia 6.1 (running stock Android One) and all other apps work without a hitch. So it's either a setting I flipped somewhere in Signal and I can't find (arguably a symptom of a bad UI), a bug in Signal or a bug in my phone only triggered by Signal.
For a while they didn't have support for front-facing cameras, but that was added some time in the last year. Only other problem I've had is that on some Android phones the "voicemail" feature (or w/e it's called) wasn't working well, but not sure if it's still a thing.