Screenshot from Obsidian:
In Obsidian, each plugin is in a separate tab so you can quickly access whichever one you need. Anytype could do something similar, but instead of each widget being in a separate tab, they would just be grouped into distinct tabs. The tab bar should probably be located below the space chooser since tabs would be tied to a particular space, but that does make it significantly uglier in my opinion.
The sidebar got really long for me really quickly so it takes a lot of time to find the things that I need. Tabs would help a lot with this since I would be able to split the sidebar into multiple tabs and then easily access the tabs since they would always be show at the top.
Another reason to implement tabs is so that people can group similar widgets or categorize them as they like. For instance, you could have the things you use most of the time in one tab, like your navigation tree and daily tasks, and in another tab your resents, favorites, sets and collections which you would only want to access occasionally.
There are no real alternatives as of now. They only thing you can do is to pile up all of your widgets in one sidebar.