since it's I/O heavy an async web-oriented stack (ie. NodeJS) makes sense, and then TS is an obvious improvement over raw JS, and if the frontend is also JS/TS then at least there's some chance that expertise can be shared
The problem is such systems are also CPU heavy, with extensive hashing, encryption, and really quite a lot of general paperwork, and as such, a system that can efficiently use multiple CPUs is really important. I guarantee that plenty of Twake installs are absolutely spending a ton of time blocked on CPU, both because of the multithreading, and the general 10x-slower-than-C you can expect from Javascript on general code.
Javascript was a poor choice that will hold the project back just as choosing PHP for the base has done and continues to do a lot of damage to NextCloud/OwnCloud. This is not a task for a scripting language, because they're disqualified on performance. It's also not a task for dynamic typing, and using Typescript can help with that, but it doesn't change the fact that Javascript is just generally slow and does not play well on multiple CPUs.
Was that because of team expertise or particular aspects of TS you thought suited the domain?