If the bottom bracket is cup and cone, or cartridge bearing, there may be slack in the bearings, that manifests as chainring wobble under load. Try wiggling the crank arms laterally. With cup and cone, you can adjust this out. With cartridge, no, that's my one issue with square taper cartridges. There may also be spalling (pitting) at one point on the inner (spindle) or outer (cup) race on either of the above. Try wiggling the crank arms at every point of rotation, at every "half-hour" mark, so 24 different positions; The spalling may be in a very small zone. This is why, with square taper, I would move the crank arm position on the taper 90 degrees every 6 months, this will spread out and minimize wear on the spindle, though not the cups.

My current hollow spindle setup with adjustable bearing preload, makes taking out bearing slack easy. I'd try to get spacers to index the external bearings periodically, but they are so inexpensive, I'll just replace when needed. But so far, 2+ years and a lot of riding, still great.

Assuming no bearing slack or adjusted out or corrected, now check chainrings. Before upgrading, I had a cheap swaged steel chainring that wobbled, I was able to carefully correct with a large, deep jaw adjustable wrench. But that was a single chainring. Multiple rings, look to see if they are both out in the same direction, and if so, the crank spider may be off, and that's a lot more difficult to correct. You may be able to use very thin washers at the chainring bolts to correct, but note it would be opposite for inside and outside rings on the same flanges, assuming equal spider flange thickness.