I don't have experience with the Sigma 105 OS, but I do have experience with the Sigma 150 OS and the EF100L. I was never very happy with the OS in the 150 and on the R5 it doesn't work well with IBIS. Most of the time I get sharper pictures with the OS (and as a consequence IBIS) off.
With my copy of the EF100L I had similar issues, the IS seemed to work a lot better on my RP than on my R5. I have had a few people mention the same issues, but >99% of the EF100L+R5 users don't seem to notice it.
My copy of the Sigma 150 is very, very sharp. Even with a Sigma 1.4x teleconverter it is sharper than my copy of the EF100L. I expect the Sigma 105 to be the same.
I haven't noticed any issues with AF, but at macro distances AF on the R5 isn't as amazing as it is for normal distances, regardless of the lens used. I don't think there will be a big difference between the Canon and the Sigma.
I haven't tried the faster drive modes, it could be that the R5 will limit the fps on the Sigma. The Sigma predates the Global Vision line, so it has no firmware updates available. The EF100L is from 2009, which predates the introduction of downloadable firmware updates in 2012. So with both lenses you are stuck if there's an issue.
I didn't like the EF100L on the R5. So much so, that I sold it and bought the RF100L. I don't think the RF is worth the price, but I am back to enjoying using the 100mm instead of hating it
Personally, I would lean towards the Sigma 105 and use it with OS disabled if it would give me issues. But I also realize that encountering, on the whole intetnet, only 2 other people seeing the same issues with coordinated IS on the R5 makes me an outlier. Both lenses are good macro lenses, the EF100L integrates better into the ecosystem with things like lens corrections. The Sigma will likely show onion rings in the EVF till you disable peripheral illumination correction.
I don't think there's a wrong choice in your dilemma