Potted posts: https://foxhollowcottage.com/diy-planter-pot-poles-for-cafe-string-lights.html

I saw this idea somewhere and it looked DIY possible. The woman's hubby used square wooden posts and cemented them into the bottoms of large planter pots. He then put a hook/loop on the tops to hold the light string. They filled the remaining portion of the planters with potting soil and planted annuals around the tops of the pots. So they basically got the patio lights placed where needed and decorated the space at the same time with flowers.

Very much like the potted pipe idea.

If you can find several wide based plastic christmas tree stands and use PVC pipe with eye hooks or other hardware to hold the wires, they would be more lightweight and portable. They'll even hold a 4"x4"x6' treated post for solar lights and/or bird feeders and/or wind chimes and/or lightweight decorations such as flags (and/or, IF weight is balanced, flower hanging baskets). I'm using a pair I found at thrift stores. (The third broke when a bear knocked it down the hill to get at the sunflower seeds in the feeder.)

https://www.mercari.com/us/item/m46184555388/?gclsrc=aw.ds&&utm_source=google&utm_medium=cpc&utm_campaign=12877497088&utm_content=t0&adgroup=121903074456&network=g&device=c&merchant_id=154841987&product_id=m46184555388&product_id=530459451263&gclid=EAIaIQobChMIgMK58rXg8AIVSv_jBx1mxQmWEAQYAyABEgIX_fD_BwE

Attaching some of the lights to your fascia and porch light so they come on each time you turn on the porch light is worth considering.

If you want to light up the yard beyond/below a deck, you could to attach lights to the deck rail just beneath the top board with cup hooks or eye hooks.

Depending upon the way you choose to hang them, inexpensive (Dollar Tree) binder clips could help you hold them into place.

If you have anything metal to which you want to attach them, you can also find in the same school/office section magnetic clips that work well for refrigerator magnets with clips. Adding a small piece of metal to wood could enable you to have more use options for them.

A half decent carpenter can securely attach custom wood posts to your deck that match and at half the cost of the string light support poles you are seeing online. Cheaper than potted cement poles too after all the ingredients for those are assembled.

I witnessed a DIY cement potted string light support project once. They ended up in the garbage before the lights were even strung.

Buy an outdoor umbrella frame, only. String lights on it.

$52.00 at world market.

@Christopher C Nc - Hmmm…I’m a halfway decent carpenter! Well maybe not HALF, but decent for sure. But I can’t figure out how to solve for the inch or so of railing hanging over the post. Do you have a thought about that? Maybe notching out the part of the post that hits where the railing is?

I'm a gardener and only a 1/4 decent carpenter and without a picture of your deck and railing I have no clue how to fasten it. Post a picture. Surely there is a fine carpenter on the premises.