I've been taking pictures and editing them with good results through Lightroom Classic and Photoshop since a couple years. I usually use lightroom for most of the editing, and photoshop for stuff like focus stacking, exposure blending, the orton effect etc etc. I always export with lightroom, no issues, the Jpeg looks like what I see in lightroom.
Recently, I started looking into printing. I found a company which will do it for me, I only have to send them a file. They have a video procedure of how to prepare a file for them to print.
They advise opening the "finished" picture in photoshop, convert it to 8bit, and do a custom preview with their color profile to then apply it to the image. I do all this without issues, the image looks a little different than before applying the profile but it's understandable why. (By example, for a glossy c-print they loose like 5% contrast).
However, when wanting to export the picture from photoshop as a jpeg like they show in their protocol, it looks completely different. The colors are completely distorted in a comical way. I really don't understand why.... It should export the raw as a jpeg that looks the same as the preview no ?
Their workflow (if I can be so kind) is not fully color-managed. They want you to soft proof with the profile (using what rendering intent?) but not convert to that output color space with the profile which is a bit wonky but expected with such labs.
If you actually exported the image in that color space, it would appear as you saw it soft proofed but that's not what they are asking for I bet.
Do they ask you to export the JPEG in sRGB or maybe Adobe RGB? If so, when you view that in a color-managed application like Photoshop, it will not match the soft proof you saw in LR using their profile although it shouldn't look 'distorted in a comical way' so we need to know more about what you're doing FROM Lightroom Classic export (what color space are you using?).
Are you perhaps using the Edit in Photoshop command? That's another issue. There currently IS a bug, resetting preferences in Photoshop should fix this for the time being. However, the bug messes up the embedded profiles from the edited images from Photoshop. So you'll need to open them in Photoshop and Assign the ICC profile you selected in the LR preferences (Edit In Photoshop prefs). So if you asked for say, Adobe RGB (1998), you'll need to open those images and use the Assign Profile command, pick Adobe RGB (1998). Now they should preview correctly. If you can save a copy of the preference from Photoshop before resetting, it would really help Adobe find a fix. Please see this original thread about this issue and if possible, provide the original preference file to Adobe as requested here: