Oath & interview on the same day doesn't sound correct. Pre-covid, in-person test followed by interview was the norm.
Pre-Covid same day oath, same as day of test and interview, was fairly common. Not for most applicants but for many. This was especially common for iterant services, but at least in the GTA this was also done quite often.
My sense is that IRCC will migrate in that direction again, as more or less normal procedures are resumed.
While mine (an iterant services case) was not the same day, I got a notice for the test (even though I was test exempt) and interview, and the notice for the oath, together. My interview was scheduled for a Tuesday afternoon, while my oath was scheduled for Thursday morning. Oath was contingent on outcome of interview of course. Many others at my oath ceremony had been tested and interviewed during the preceding two days, Tuesday and Wednesday.
(In addition to the interview, I also had to respond to a telephone inquiry during the Saturday prior to the scheduled interview; during that telephone call I asked about the notice for the test and was assured I would not be taking the test, and I didn't -- I was only slightly concerned about having to take the test, only because I had not studied at all for it, being way over the age for the exemption, but otherwise confident I could pass it since I had been living in Canada for most of the previous decade and a half, and my Canadian born wife more or less mandated, at least in part, my becoming a Canadian, not on paper or in name, but fully immersed in all things Canadian.)
By the way, pre-Covid ALL adult applicants were interviewed, and this was almost always attendant the test (online tests were only implemented in the latter part of 2020, due to Covid), interviews generally immediately following the test.
The PDI outlining the citizenship application process still lists the interview as a necessary step for all adult applicants, even though this has not been necessary for a large percentage of those who have taken the oath in the last two years. Odds seem to indicate IRCC will get back to requiring all adult applicants be interviewed. And doing more same-day (or following soon after the test and interview) oath ceremonies.