Try oil lemon oil or teak oil or mineral oil. I hope you haven't tried anything else. Oil works but it is easier if it is not altered by other chemicals. Cooking oil is good for removing label and price sticker glue from glass or ceramics too. In fact almost any kind of tape glue is removable with oil--something to keep in mind for the next time you want to remove tape glue. Since I found this hint it's the only thing I use.

I found this on https://www.gsa.gov/portal/content/113602 Removing Linoleum Adhesive From FloorsProcedure code:965001SSource:Ohj - Shirley Maxwell & James C. Massey, 9/30/92Division:FinishesSection:Resilient FlooringLast Modified:08/02/2016 REMOVING LINOLEUM ADHESIVE FROM FLOORS PART 1---GENERAL 1.01 SUMMARY This procedure includes guidance on removing the mastic adhesive left behind when linoleum flooring has been removed. Linoleum flooring was very popular from 1863 to 1974. It was used historically as an original floor treatment in some GSA buildings. Linoleum's chief ingredient was linseed oil, pressed from flax seed, which became a tough, elastic material when exposed to air. The process essentially consisted of mixing linseed oil and gum with ground cork or wood flour, and pressing it onto burlap or canvas. It was then glued down to concrete or wood floors using a mastic cement. See "General Project Guidelines" for general project guidelines to be used along with this procedureThese guidelines cover the following sections: Historic Structures Precautions Submittals Quality Assurance Delivery, Storage and Handling Project/Site Conditions Sequencing and Scheduling General Protection (Surface and Surrounding) These guidelines should be reviewed prior to performing this procedure and should be followed along with recommendations from the Regional Historic Preservation Officer (RHPO). PART 2---PRODUCTS 2.01 MATERIALS Clean, potable water Vinegar Citrus degreasing solvent such as "Limo Sol", or approved equal. Dry ice Chemical solvent such as isopropyl alcohol, paint thinner, xylol, lacquer thinner, or paint stripper. 2.02 EQUIPMENT Heat lamp or hot-air gun Putty knife or scraper PART 3---EXECUTION 3.01 ERECTION, INSTALLATION, APPLICATION NOTE: A waterproof glue is usually applied at the edges and seams of the linoleum; the center of the felt layers is usually attached with a water soluble paste. Soak the mastic area in hot water for 20-60 minutes or until soft.\ If this is not effective, try adding vinegar or high-strength citrus degreasing solvent to the water and then soak for 20-60 minutes until soft. If mastic still will not soften, try applying heat to the surface using a lamp or hot-air gun. -OR- Try freezing the mastic with dry ice to break the bond with the substrate. If no other methods are effective in softening the mastic, test a chemical solvent on the area. NOTE: Be sure to test in an inconspicuous area to determine appropriate chemicals and strengths before proceeding with cleaning. Scrape away the softened mastic using a putty knife or garden edger. END OF SECTION interesting................

We have cats and litter boxes......and 1920 wood floors....... Since the cats are staying we decided to Paint the small area under the litter pan(s)........a Litter "Welcome Mat" Preparation is key.....we cleaned and enzymed........Sanded.....Caulked all seams(floorboars and baseboards) with a strong URETHANE caulk (paintable/solvent based).....and then followed with a good brand of Oil-based paint.......(Latex caulk/paint will dissolve in contact with urine....) It's been almost 10 years (so we're still Beta testing) ......the floor cleans up easily with no lingering odors......we generally leave a small amount of litter on the floor under the pan to absorb any "misses".......when the paint needs attention we just mask and recoat with the same oil-based product.

M., sorry, this isn't mine. just using some pics to show you examples. the 2nd photo is a red oak, completely sanded and done w/a natural finish. You'd be surprised at how beautiful old wood floors finish up! Call in a professional wood floor refinisher and get some estimates. it won't be an issue to match your existing solid wood flooring. https://www.svbwoodfloors.com/blog/wood-floor-faqs-whats-the-difference-between-a-lace-in-and-a-header/ here's a video https://www.youtube.com/watch?v=RDqi5NAnTKk look at this before and after https://adamsfloors.com/installation