I have heard folks claim that 90-degree MC, or flex, fittings had to be treated as an LB would be treated, and remain accessible.
Personally, I do not share this opinion. I do concede that some such fittings have little covers that make them resemble conduit bodies, but I still do not consider them to be the same as conduit bodies.
As for straight connectors .... I'm not sure it's possible to use them without concealing them. The NEC clearly allows for fishing the material ... and it's been quite a while since I saw a box with internal clamps.