I wonder whether they support Ethernet bonding on the SXT LTE hardware ?
There is definitely support in RouterOS, but I couldn't find anything to say whether the SXT LTE can do it on its two ports.
Not really an issue for me, my LTE tops out at ~80MB.
802.3ad bonding is a software thing in the OS. It is only a "hardware" thing on switches and even then it's actually a software thing in the switch OS. So the short answer is you almost certainly create a bond given support in a suitable switch.
On the other hand what most people fail to understand about ethernet bonding is that a single connection will always
make use of a single link in the bond. So a single device on the network will only ever get 100Mbps, you would need a second device to get to 200Mbps.
This limitation is generally not that important when creating switch to switch interlinks or when connecting servers to switches because it is a reasonable assumption that you will have multiple connections going over the links so the speed limit on the individual link is not so important. I would note this limitation with ethernet bonding is why Microsoft created multichannel SMB.
I imagine the hardware will need to be redone for a 5G version however as a 100Mbps limit would be suboptimal.