You are welcome. Glad to help.
Yes, I always varnish my work. I work in oil so it makes the final art look better and gives it a unifrom sheen. I also work in watercolor but do not varnish them, although I could. preferring to frame them behind plexiglass.
It has been a while since I worked in acrylic so I am not as up to date on what to use. I used to coat them in a clear acrylic matte medium. Not a true varnish but that would allow me to paint back on top with if I decided to.
You have to keep in mind once you varnish you can NOT rework on top without removing the varnish first. This means delicate works, like watercolor, mixed media, works on paper etc it is too hard to remove, separate, the varnish from the media to rework. Once you varnish it is done.
Paintings in oil and acrylic that don’t have the ground exposed too much, the ground being paper or some illustration boards (paper surface) can be varnished and the varnish removed if necessary.
Of course you have to select a varnish that is removable.
For a varnish to be removable it has to be chemically different than the medium otherwise the remaval of it will also remove the medium (artwork) and you don’t want that.
Select a good conservator archival varnish.
You said you don’t want to spray varnish. I prefer it because it makes me nervous to physically brush across the art. I spray because it is a more passive application so I never have to touch or drag across the painting. I have sprayed up to medium sized paintings (24x36") without too much trouble. After that I have to brush it because it’s too big for a spray can. One of the 24"x36" paintings I forgot to sign so I had to remove the varnish in one corner, sign it, then respray the varnish so I know THAT works.
I use the Krylon UV Archival varnish in the link below.
I use a satin because I hate the glossy/high gloss glare with anything else. I find it a distraction when I go into a gallery, am looking at paintings and to avoid the glare I have to duck and move back and forth to actually see the whole painting.
https://www.krylon.com/en/products/clear-coatings
I also want to point you to this link which is more specific for acrylics. Mod Podge might be a good one for you based on your comment.
https://www.abstractart.live/blog-krmoehr-art/ha50u6e07638442vqs380v2p03bjg1#:~:text=Best%20Ways%20to%20Seal%20an%20Acrylic%20Painting&text=The%20best%20way%20to%20avoid,surface%20you%20are%20painting%20on.