I got everything updated.

fabric-api-0.44.0+1.18.jar
fabric-installer-0.10.2.jar
optifabric-1.12.9.jar
OptiFine_1.18.1_HD_U_H4.jar
replaymod-1.18.1-2.6.3.jar

I get this

If I remove OptiFabric, it loads Fabric & ReplayMod with no problem. Second I toss OptiFine in, everything goes pear-shaped.

Now, if I delete OptiFine, it naturally gives an error wanting OptiFine. So I know SOMETHING is working.

I've removed ALL the mods and redownloaded them to make sure nothing was corrupt to no avail.

My profile is the latest

It won't work with replay mod, I don't know why exactly but that's it.

Yup, you're right. Not sure how I missed that. What a bummer. Kind of needed that one too. Ok, so ... I'll move this over to ReplayMod's Discord. Thanks, stomno.