After several months of experimenting with OpenWrt on the Raspberry Pi 4B, I've come to the conclusion that OpenWrt is the last remaining useful application for this now outdated and slow device. It can very easily be set up as a wireless router, a wired router, a travel router and all of these can be easily configured to optionally use OpenVPN clients.
I've messed with this device for over a year and I've yet to get it to reliably run as a useful desktop computer under Raspian or several other Linux variations claiming to operate on the Pi. It's too slow for that. I can't even get the thing to display the GUI on my TV or Dell monitor properly. All the tweaks to fix this don't work anymore. The OS without the GUI is pretty solid and I can create a home VPN server that is super reliable running PiVPN. Aside from that, only OpenWrt is a practical use of this small device.
I'd have to say you probably don't want to use it as your main router but you could very easily. I think the absolute best use of it is to place the device between your modem and your main router with Ethernet and with OpenVPN configured. In this way, your regular router will operate normally, but the Pi is always going through the VPN providing Internet to your main router. If you don't want to use a VPN, you can also easily configure AdBlock so your main router works normally, but the ads are blocked by the Pi. Variations on this are easy to imagine. You just need one Ethernet dongle since the Pi has just one wired connection. VPNs are slower than the speed penalty the use of the Pi might cause.
Making a wireless router is even easier when internet is connected to the single ethernet port and the built-in wireless provides wifi. Just a little hassle re-configuring the one Ethernet port as the wan, but it's simple. You can add OpenVPN to that too if you want. Plug it in to your router and just connect to the Pi's wireless and you're behind the VPN with no software running or needed to be configured on your computer.
The travel router is a little more difficult, because you need to get a second radio via a wireless dongle - and these dongles don't work reliably a lot of the time and the built in wifi is slower than it should be. However, it's not like free wireless is providing high speed internet anyway. Adding the OpenVPN layer here is likewise simple.
A wireless bridge is easy too where you have a device that needs an Ethernet connection and has no wireless capability, the built in radio can get the wifi and the Ethernet port is already configured to provide a lan connection.
This is the magic of OpenWrt - it's configurability and utility for multiple applications for so many setups. And the Raspberry Pi 4 which is now a legacy bit of hardware still operates very well on OpenWrt.
I'd be interested in any comments about your novel use of a Raspberry Pi 4 different from these because the are so many creative people out there in this forum who solve problems. Tell me about the problems you solved and how you've applied OpenWrt. There is a learning curve for OpenWrt, but the maze can be navigated with the help available on the forum.