Linked layers / virtually merge layers in QGIS?

I have 20 different regions (let’s say 20 provinces). For each province I have let’s say 50 different attribute tables / layers containing data for the province (roads, bridges, towers, …). I would like to show the Data for all provinces in one QGIS file. So I have to import all these layers into one QGIS file ending up with 20 road layers, 20 bridge layers, 20 tower layers,….
This brings up 2 problems:

1. Due to the amount of layers it is extremely confusing to work with the file even if I group them.

2. When I change the symbology of the tower layer I have to change it 20 times, right?

So what I did was I merged the road data, bridge data, tower data into one attribute table each, ending up with one layer containing the roads of all provinces, the bridges of all provinces, the towers of all provinces. Working with the file now is more easy due to the extremely reduced number of layers and when changing layer symbology e.g. for towers I only have to do this once.
The problem is though that when I get updated Information on a province I have to manually merge the data with each attribute table again (new infos on roads, new info on towers ….), deleting the former information in the related tables which all together takes a lot of time and is confusing and error-prone.

I hope this was so far understandable.

What could be a solution is to put all the data (shape-files) in a folder on the harddrive and just virtually merge them in QGIS, like they were just linked. They would show up as one layer in QGIS but the referred data lies separated on the drive. When there is new data available for one province I would then just replace the files in the folder on the harddrive and next time QGIS starts, the virtually merged / combined / linked table would contain the updated information.

Is there a way to do this in QGIS?

Or is there another way of handling this? One way would be to have separate QGIS files for each province which would be my dream anyway, since working with the file is really slow, and saving the file takes ages. But the problem with this solution is that we quite frequently have to change layer symbology. Each time we change the line weight for roads you would have to open all files one after the other and change the line weight of the road layer to be consistent (at least as far as I know there is no other way). This is not acceptable. Does anyone have a solution following this path?