Nah, there's no monthly quota. The bottleneck is probably a combination of the upload speed of your broadband Internet service provider and network congestion (primarily how many devices connect to it).
I signed up for iTunes Match a year or two after it debuted (10+ years ago?). I had a decent sized library (400 GB? 500 GB?) and it took 10-12 days of uploading (mostly while I was at work or asleep) on my ghetto connection. My match percentage is currently something like 80-85%.
However, my initial iTunes Match sync happened in an era when cloud services were pretty paltry so less traffic. Today's cloud services generate tons of network traffic, especially if your network connection is sharing bandwidth with more devices (more mobile devices, smart home appliances, media streaming boxes, smart TVs, HomePods, etc.).