Web-Editor chokes on larger texts (performance issue)

Describe the bug
Editing (e.g. marking a word and making it bold) is slowed down significantly, when the text is big.

To Reproduce

1. Visit NextCloud in browser
2. Click on "New Text Document" and enter a name
3. Copy a larger chunk of text
   3.1. e.g. visit https://en.wikipedia.org/wiki/History_of_England, CTRL+A to mark all text, CTRL+C to copy
   3.2. CTRL+V a couple of times in nextcloud
4. Mark a word and click on b/bold
5. Alternatively, mark all text in the markdown viewer (e.g. mouse-based, or CTRL+A) and do the same.

(Notice the lags.)

Nextcloud version: 18.0.6

Browser log

In my case, the sync POST request shows ~1 KB of data. After clicking on the "make bold" icon, it takes a second until the text is displayed in bold (and a 806 byte push event). The longer the text, the more laggy does the UI seem to be. I had a user jump back to google docs because of that :( . The same text felt snappier in Collabora Online/Office.

It seems that the lags occur through client based processing, as push event is shown in the network log only after the second(s) of delay, but here I do not have enough insights into how and when the logging is done (only after all processing?).

Reproduce the lag in the browser editor by pasting a large text and applying bold, then inspect the browser log and network activity around the delayed sync POST and push event. Trace the client-side processing triggered by the bold action. Done means large documents remain responsive while formatting and the related events still complete correctly.