First of all a disclaimer: I am not upset about the removal of manual server selection as this is a free service. They don't need to provide such services at all, so something is better than nothing.

What happened:
This morning I opened the ProtonVPN app on my phone and got greeted with a message stating free accounts can now only use automatic server selection and addition of free servers in Poland and Romania.
However, I also noticed split-tunelling is now paywalled as well.

Now, this is rather weird. Split-tunelling is already in the app and is something that works only on the client side, thus not putting any extra load on the servers. Quite the contrary, actually, as it allows some apps to not use the VPN, thus use less bandwidth.
The automatic-selection-only allows for better load balancing, so that makes sense.

Now to the workaround.
They still allow manual OpenVPN and Wireguard setup even for free accounts, at least for now.
To do so, login to ProtonVPN and go to account. There's OpenVPN credentials which are used for OpenVPN authentication. Then go to downloads, select appropriate options including the specific server and download the ovpn config file.
Client: OpenVPN for Android
This app also supports split tunneling (edit config -> Allowed apps).

ProtonVPN has an article on how to set up this app, but it's really just importing the config and adding your OpenVPN ProtonVPN credentials which you grabbed before.