Protein bands not visible after sds page coomassie dye stain
The problem here is concentration. Coomassie Blue stain can only detect protein band greater than or near to 50ng, in this case, the concentration of your protein is too low for detection. If you want to stick with Coomassie stain, you can try colloidal Coomasie stain instead because it has a much lower detection limit than Coomasie blue (between 10ng to 20ng).
In addition, I think what causes such low protein concentration is the poor solubility of yeast cell wall. One way to get around this is to increase solubility is through chemical hydrolysis, for example using diluted sulphuric acid1-3. This will partially solubilize mannas-protein outer layer of the cell wall and help you to obtain soluble yeast cell wall products.
References:

Theodoro, S. D. S., Putarov, T. C., Tiemi, C., Volpe, L. M., de Oliveira, C. A. F., Glória, M. B. D. A., &amp; Carciofi, A. C. (2019). Effects of the solubility of yeast cell wall preparations on their potential prebiotic properties in dogs. Plos one, 14(11), e0225659.
OGAWA, K., &amp; MATSUDA, K. (1994). Characterization of Manno-oligosaccharides Containing α (1→ 2)-and α-(1→ 6)-Linkages Obtained from Saccharomyces cerevisiae Mannan by Controlled Acid Hydrolysist. Journal of Applied Glycoscience, 41(4), 433-437.
Peat, S. (1961). Polysaccharides of baker's yeast. Part IV. Mannnan. J. chem. Soc., 61, 29-34.