Questions: what is the railing on the left side, what functions do you want this area to have, do you want to expand the deck area, cover it , or keep it as is which appears to be concrete, what planting zone are you? Thx.

If you have a one step high deck I don't think you need a railing but you should check what the rules are in your area. I'm suggesting a pergola over the deck with a dining area and seating area.

I prefer decking to patios but a lot depends on how you will use the spaces . How do you entertain outside ? Where do you BBQ? How many people do you have on a regular basis for seating.? I like an outdoor area to be layed out like a home , so a kitchen (BBQ) a dining space and a LR (seating ). I think you plan any out door area for how you use it so answer some of those questions and we can help a lot more .

The place to put a small tree is so it will provide shade for your deck. For morning shade, to the E/SE. For shade from the hottest sun of the day, W/SW.

Some option to go with pergola

We enjoy using sun sails to shade in the hot summer and take them down in the fall so our sunroom gets more solar warming then. Consider how a pergola will change the light through those windows. Like Sigrid I need colorful pots of sweet smelling herbs and flowers. Little tables to set a cold drink can be a simple as a couple cinder blocks and a paver. Add some solar lights for evenings. Citronella candles and solar bug zappers if you have mosquitos.

I think you need landscaping and agree with a tree as @laceyvail 6A, WV suggests. Just remember it takes several years for the tree to provide shade. Ask me how I know lol. A concrete pad on the left for a grille. An enclosure for the AC. Maybe a retractable awning.

An outdoor oscillating fan cools things down and keeps away mosquitoes - we’ve had one from deco breeze for years

And while a shade cloth or retractable awning is better than nothing, nothing compares to the leafy shade a tree provides. Plant the tree--proper size for the distance from house and patio--and plan ahead.