I created something like what you're describing with the addition of P2P communication using NAT traversal (https://www.hyperpath.ie)

It will connect your devices in a P2P Mesh VPN and allow them to send and receive data using multiple links (e.g. multiple 5G or 5G + Satellite).

It is significantly cheaper than Peplink's license, less latency and no bandwidth / data limits.

You need to bring your own hardware though. Like a Raspberry Pi with 3 USB 4G/5G dongles.

what about something like this? two minipcie slots which i suppose you could put two cellular modems into. not sure what OS it runs though but presumably some flavor of linux.

https://mikrotik.com/product/rbm33g#fndtn-specifications

maybe someone could make one that uses an RPi compute module instead.

It looks like it runs "RouterOS" which has a Linux kernel, so it should be possible to run it there.

I found this board on AliExpress (https://www.aliexpress.com/item/1005003540616473.html?spm=a2...) based on the CM4 and with 3 cellular modems. That could also be a good candidate.

Also found this one (https://www.gateworks.com/products/industrial-single-board-c...) US-made and has 3 minipcie slots (other options available with 2 and 4)

Hehe, I also worked on a delivery robot with exactly the same problem. We ended up licencing phantom auto. Expensive and ... Not particularly amazing.

How was the connectivity with Phantom Auto?