Most tripod heads have a means of turning the camera from horizontal to vertical orientation. However, due to the designs of many tripod heads, doing so often makes for a somewhat unbalanced rig with the weight of the camera and lens flopped over to one side. It depends upon the specific head and tripod... some are better in the vertical orientation. But a lot aren't.

An L-bracket can solve this by allowing means of mounting the camera either horizontally or vertically. One "catch" is that you typically would want to be using a tripod head with an Arca-Swiss compatible quick release platform, as the vast majority of L-brackets are designed to be work with that. None I'm aware of are designed to accommodate any other type of QR system. But most L-brackets also provide standardized 1/4" threaded sockets to mount on tripod heads that don't have any QR.

There are "universal" L-brackets, but they can be a problem blocking some features of your camera, such as memory card and battery doors, various sockets for cables, or controls.

Better are L-brackets designed for a specific camera, which have cutouts that allow access to all the controls. In your case search for "Canon R5 L-bracket". If you have a battery grip (BG-R10) on your camera, it requires a different L-bracket than the camera without a grip. These fitted types of L-brackets may cost more but also typically have much better anti-twist features to prevent the camera from rotating and loosening from the L-bracket.

Personally I'm not a big fan of L-brackets and don't use them on most of my cameras. The good L-brackets usually ain't cheap and they add bulk to the camera, which is particularly noticeable with my larger DSLRs that have a battery grip installed. I have Arca-compatible camera plates on them and other means of mounting the camera vertically, if needed (specifically, a side-mount gimbal adapter... Wimberley Sidekick... though I primarily use that for it's original purpose).

However, I do use an L-bracket on a small mirrorless camera. Partially I do this because I plan to use the camera on a smaller, lighter weight travel tripod where the bracket is more important. Also, being accustomed to much larger DSLRs with battery grips I found that tiny mirrorless camera rather uncomfortable and actually appreciate the L-bracket "bulking it up" a little. Finally, I found a great deal on an L-bracket... Initially I was looking for an Arca-style camera plate for the camera. There are only a couple manufacturers making them and the prices were rather high. Then I found the Chinese-made L-bracket on a certain auction website at 1/3 the cost ($16 incl. shipping) and decided to give it a try. When it arrived after about a week I was very pleasantly surprised at the quality and fit of this bracket. It's even modular! I can remove two screws and convert it to a camera plate if I wish. And that tiny camera now feels more comfortable to me... and will be more stable when set to vertical orientation on a lightweight "travel" tripod.

I partially disagree with another response: There's little direct relationship between flash mounting brackets and L-brackets. There may be some "combos", but in most cases they are two different types of brackets that serve two different purposes. There ARE modular flash brackets designed to work with Arca-Swiss camera plates, lens plates and L-brackets. For example, I use several of Wimberley's flash bracket modules. I also have a several flash brackets I've customized to attach to Arca camera plates or L-brackets. And, yes, there are some flash brackets that allow reorientation of the camera and flash. Or in some cases even can facilitate vertical mounting of the camera on a tripod head. However, generally speaking L-brackets and flash brackets serve different purposes and have existed side by side for many decades.

Various types of brackets have been common in photography for just about as long as there has been photography. In addition to flash brackets and L-brackets, today we have "cages" that some videographers like to use, to allow various accessories to be attached to a camera (mikes, external viewfinders, grips, etc.). Back in the day there were "grips" that could be attached to many medium format cameras. Personally I have those for several vintage cameras in my collection... most do not help with reorienting the camera, but in some cases provide a mounting point for a flash and/or a shutter release. There also have been flash brackets with left-hand grips for 35mm SLRs offered for many years.

"...if you walk into B&H, Adorama, or any large metropolitan area camera store, you're likely to see a dizzying array of gizmos that make certain photographic efforts easier..."

That's certainly true!