The test images from Agfa Isolette turned out unsharp, very unsharp. I have no 120 film scanner, so no image to show. Could the distance adjustment be out of order? All images were strange enough correct exposed.
The Isolette is so straight forward it must be the lens mounting, are there signs it has been tampered with?, or the front element focusing got at? I assume the front opens correctly etc. There's no more serious problem possible, the lens is three element, so no glass to unstick etc. Damage to the body back should be obvious.
Assuming a normal Isolette model, the scale on the focusing is almost flush with the front at infinity focus, maybe the focus ring has the small retaining screws loose, and the scale reads right, but is not turning the front unit to the correct positions. Some models may not have screws, but usually do.
Cure is to ensure the focus is really at infinity with a ground glass, and then adjust the front focusing scale to match.
If you have no ground glass, greaseproof paper will work, taped to a piece of plain glass, or make your own ground glass, with car valve grinding compound, the fine grade, rubbed into the glass surface in figure of eight motion till smooth matt finish. Randomise the polishing motion as much as possible to get an even finish.
If you have a flat bed scanner, the negs can be laid on the plate and will scan, test with cover open as well, or with a piece of paper above the neg (to diffuse the light), back illuminated, and scan at maximum settings. Some flat bed scanners are better than others, the Canon LE ones work well.
Also as the 120 neg is large, most Digital cameras on Macro should be able to take a shot, then reverse to positive in Photoshop etc. Illuminate from behind with paper diffuser, say taped to window against sky lighting.
The Isolette 2 (1950's) definitely has retaining screws in the focusing mount at the front, which is not flush as the earlier ones, which have a different surround to the scale. These screws coming loose, or having been tampered with, are the most likely fault. Should be an easy re-set job. I would expect pin sharp results from the Agfa at medium apertures, perhaps a touch soft at maximum aperture only. Stephen
Study on the net shows lots of minor variations to the Isolette focus ring, there were lots of small changes, some even have an open screw to act a stop at infinity, if this is yours, then the open screw could have been removed and replaced the other side of the stop, giving the wrong focus range completely.
Some have a flush edged ring with just one tiny screw retaining it on a screw ring inside, some appear to have three tiny screws which indicate a drop on ring, the position set purely by the screws.
At these cameras age, it is not unlikely it has been tampered with, a lot of 120 folders were left out of use, and then given to youngsters to use or play with etc, they may well have been got at over time.
You have found the problem, the distance scale turns but the lens stay in the same position. When focusing at infinity it should be travelling towards the camera, but there is no movement. It seems the lens is stuck in some way as it is not will turn any way.