Cleveland is an odd case where HRT and LRT already shared track, and ridership that doesn't need the capacity of HRT. Pre-COVID ridership was about 18k on the Red Line and 5k on the Green + Blue lines, compared to 69k for the Blue Line.* I don't believe the Red Line regularly used trains any longer than 2 cars. The system also needs minimal modifications: the lines already share a maintenance facility and catenary, and they're buying high-floor LRVs with movable steps so no major platform modifications are needed. So they get the benefits of a shared fleet and the ability to interline services, with no real drawbacks.
The Blue Line would require major station reconstruction (or high-floor LRVs incompatible with the Green Line and making new surface stations more expensive), new catenary in the tunnel, modifications to the maintenance facility, and so on. It was already having capacity issues pre-COVID, so you can't make the trains any shorter unless you substantially increase frequency, and modern LRVs might now even fit the narrow-profile tunnel. The idea of branching and a cheaper surface extension are tempting, but I can't see LRT conversion being practical or useful.
*Cleveland and San Juan, which has a host of problems, are the lowest-ridership heavy rail systems in the US at 18k. Next are Staten Island at 21k (converted to HRT in anticipation of hooking into NYCS, and kept that way for rolling stock commonality), PATCO at 38k (more of an electrified commuter rail line, and maybe should be converted into one), Baltimore at 38k (goes nowhere), and Miami at 59k (big growth in the last few decades despite poor density). After that there's a big jump to the major systems, from LA at 129k on up.