OK, good that it's known, but I couldn't find any reference to it here on the forum. New users of Arduino won't neccessarily know about GitHub.
That's perfectly fine. The forum is the best place for people to have discussion and request help. We can be more "chit chatty" here than would be appropriate for GitHub, where there must be a tight focus on the software development work to allow the developers to be productive.
I always try to link to the relevant GitHub resources during discussions here on the forum so that the participants can know that it has been reported to the developers and have access to any useful information that might be available on GitHub. Conversely, when things come up here that have not yet been reported to the developers, I often suggest opening an issue on GitHub, and will sometimes do that myself if the OP is unable.
So even if there is some redundancy between the two worlds, I think they are able to work symbiotically for the most part with a little help from some "bridges" who dabble in both worlds, such as myself.
For now, I have switched back to the older version.
I'm sorry to hear that the IDE 2.x was not able to meet your requirements in its current beta development state.
I think this issue is a bit tricky due to the modular architecture of the new IDE. Unlike the classic Arduino IDE, the IDE 2.x code base is exclusively concerned with the GUI, and even that modularized by using the Eclipse Theia IDE framework for the universal elements, with an extension to provide the Arduino-specific customizations. All the non-GUI tasks are handled by separate tools. In the case of the Serial Monitor, this is done by Arduino CLI. There are some huge benefits to this approach vs. the original monolothic (translation: nightmare to maintain) approach used in the classic IDE's Java code base, but it seems it does introduce more potential for bottlenecks in the transfer of data between the components.
Fortunately, Arduino has some very talented people working on this problem, so I'm confident we will see some improvements on the situation in upcoming releases. And of course it's open source software so the entire Arduino community has the opportunity to lend a hand to improve this tool.