While Teltonika devices do not offer an adaptive link rate option for SQM directly, they do basically use the SQM package from OpenWRT, which means you may be able to utilize OpenWRT solutions.
There is an interesting thread on the OpenWRT forums here where a custom development solution is available to enable adaptive bandwidth management with CAKE. This custom package is hosted on GitHub, which also provides installation and usage instructions.
Given that your RUTX50 runs RUTOS, which is based on OpenWRT, you should theoretically be able to install and run this package, although I have not personally tested this. Thus, I cannot guarantee that this will work. If you choose to try this solution, it would be greatly appreciated if you provide feedback on whether it works for your situation. Please remember that custom solutions like this may come with additional complexities and potential risks.