This was discussed in the past on https://bugs.chromium.org/p/chromium/issues/detail?id=487017

It's come up again for new display assistant devices, for example
(1) existence of touchscreen but no keyboard means that users can focus elements, but focus doesn't do anything. The focus outline is distracting as a result.  (see internal b/111486026 for more details on that).
(2) touchscreen allows selection, but there is nothing a user can do with the selection. Disabling selection highlight in css is apparently the simplest solution.