Can I use TWP100 on this old deck

My question is about the appropriateness of TWP100 on my old deck and an ancillary question about repairs

I refinished a 7 year old cedar deck in 2020.  It had a peeling semi-transparent stain.  After stripping brightening, and sanding I used a penetrating oil sealer (TWP 100)

I have since moved to northern Minnesota.  My current deck is 40 years old and made of pressure treated pine.  What has protected the deck from rot is that 1) it is elevated-5 ft. off ground, 2) there is 3/4 inch spacing between planks, and 3) the prevailing breezes from the lake blow under the deck.

The deck planks, supports, and fascia have had very little maintenance; at one time the deck was painted.  The paint has substantially peeled.  The deck is weathered.  In many areas the grain was raised 1/8 to 1/4".  There are cracks, a few problems with knot holes, in 5% of the boards the crack in the central portion of the plank has progressed from a crack to a divet.

Because I am a rookie, I thought I would take on this project.  My initial plan was to prep it for a waterproof paint (ie Kilz Over Armour)

I purchased a Restore-A-Deck stripper/brightened Kit from Deck Stain Help.  I appreciate this is not for paint but I did not want to use a paint stripper as I worried about my new house siding.  I planned to sand off any old paint.  After the treatment, even with intense scrubbing and pressure washing, the deck looked pretty unchanged.  All the boards had a white residue between the raised grains.  This is partly my fault.  My pressure washer hose developed a leak just when I needed to wash off the brightener which dried on the wood-despite intensive rinsing with a garden hose.

Next I started sanding. Hours and hours and hours of sanding.  The wood despite its weathered history started to look pretty good.  I cleaned the cracks with my joint compound knife, used a dremel to clean out loose wood particles in knots and divets, and completely sanded the sides of the boards(many had residual paint).

Now to my first question: When I started to see that the planks looked nice, I began to wonder if I could avoid a deck paint and instead use a penetrating oil sealer like TWP 100  I don't mind regular maintenance which is vastly preferable to sanding.  Assuming the TWP 100 would work, how dry does the wood have to be before application?  In northern MN we are prone to unexpected showers.

My second question is on repairs  I have read your comments on the uselessness of wood fillers like Bondo  I have a few areas that could stand a repair.

I also read your comment that splits in the supports are normal  I have one support whose north facing side has a substantial split.  The surface had fraying layers of wood.  I sanded this smooth and cleaned out the split.  It was still slightly damp from a heavy rain 48 hours before.  What do you think about filling this with an elastometric polyurethane caulk?