Thinset morter, as the name implies is THIN set and is NOT recommended for leveling. Any bed over 3/16" inch is too thick....it will crack. A "mud bed" or "mason mix" is ideal for leveling a tub. I have also seen expanding foam used for this .....

I used standard type s masons mix when I did my tub. It turned out fine but I think I mixed it too stiff, which made it hard to settle into place. In retrospect, in addition to mixing more fluid, I would trial fit the tub and add some "feet" to the bottom integral rails to make the tub level. Then, as it settles into the mud, it will stop where it should. I hope your floor is not so far out of level that your flooring won't cover the gap created when leveling.

@Avant I am well aware that thinset is not what should be used. I am referring to the standard mud bed. Modified original post to reflect "mud" provided I misspoke/mistyped. A matter of semantics keeping in mind that many tub manufacturers refer to the mud bed as a mortar bed or mortar bed mix.

@Avant Sounds like I may need to level the subfloor; although, Kohler recommends 1-2" thickness. All material that I've read for multiple acrylic tubs generally recommend the same so I'm a bit surprised to see the 3/16" thickness noted.

@Seabornman Build up of flooring should cover the gap whether I choose to use 1/8" or 1/4" underlayment. My tile alone will be 0.4” thick.

Again, Mason Mix or "brick morter" works well for this. If you mix traditional floor mud, you should add a bit of lime to the mix. You now have what is referred to as "Fat Mud," which is used to fabricate curbs.

@Avanti Have you used self-leveling over OSB? If so, what brand? Assuming (maybe incorrectly) you are referring to a 4-to-1 mix as “Mason Mix”, what brand was used over the chosen self-leveling? I’m asking so that I can research any recommendations.

Certainly, "self leveling" as is available from Home Depot can be used, BUT, we are talking about a "bedding Material" for the tub. The 4 to 1 I use for making shower pans....but that is not what you need. For setting the tub, use brick morter or mason mix (same stuff) and mix it up like peanut butter consistency...but a bit "looser."

Drop the tub in and fil it about 3/4 full of water and let it set for a day or so. From there, you should be good to go....

@Avanti Respectfully, you have missed part of my inquiry. Per my three questions posed in the original post, I am considering using self-leveling to address the slope in the floor before setting the tub. Therefore, again, have you used self-leveling over OSB, and if so, what brand did you explicitly use? I am seeking alternatives to afford myself multiple options. If the answer is “No”, that’s fine. Although, please let's stay on topic We're getting further away from my original post when I am also not requesting instructions (see original post) but rather recommendations for alternative products (explicit brand names) based on one own’s experience that are OSB-friendly - provided options seem limited.
Note: As mentioned in my original post, the only lightweight OSB-compatible self-leveling that I could identify - whether at Home Depot or otherwise given I have searched brands sold at Big Box stores, smaller local or regional retailers, and online-based retailers - including brands like Laticrete - and even communicated with an array of manufacturing reps - is by Custom Building Products.